Since it's a long post: the money issue is just a means to make a foundation and build an argument for the main point in the last half: game balance/AI and design. I tend to write long ones :S
A problem which Zeinul recently addressed: there is too much gold. Currently I'm playing a Deity game, and though I started outteched big time I could just buy my way up the tech tree as soon as I shared a religion with one of the techleaders and did some sucking up. Gold had become a more or less irrelevant factor - what's a mere 2000-3000 gold for a key tech when you have over 30.000 (and more coins keep flowing into your coffers)? And after having bought your way to the top, it's easy to modernize your own civ and become the powerhouse of your age. No fancy leader (played Hittites - I think its leader is expansionist/imperialistic while I'm a builder rather than a warmonger) or a sound plan of action other than building as much stuff in my cities as possible and keeping research at 100%. Which is not much of an impressive or coherent strategy, I guess.
Even though my gameplay sucked, the game nonetheless handed out enough cash to break core game aspects like keeping up with tech. But also aspects like crime (the extra costs for watchmen are irrelevant), many events (the costs to do anything, like rebuilding a burned down forest or building, are peanuts in comparison to income), the choice whether to upgrade obsolete units or not (with lots of cash it's close to a no-brainer, effectively eliminating the choice) and the building of wonders (if others get close to building a wonder I'm working on, I just shrug and finish it by paying) are heavily affected by more or less money. Of course one can solve that money-issue by either reducing the amount of gold handed out or by approaching the problem from the other direction and modify the costs of things - make all costs depend on the amount of in-game money, for example.
But maybe it's useful to step back and look at the bigger designing picture. Its clear that in civ4 every change to the game affects a lot of other aspects. Instead of that cash-issue, one can make a similar list of effects as the one above for mechanics like hunting, rogues or the caravans-which-can-be-converted-to-hammers. When reading the posts of the modding team on the forum, lots of enthousiasm to add more and more stuff is shown, and the following decision of whether to add it or not seems to be purely decided by the mechanical feasibility of implementing the idea and the personal vision of the one programming that idea. The issue of having to keep the game as a total balanced and challenging seems to be becoming an afterthought rather than a central consideration. In one of the "fresh idea"-threads regarding some new mechanic for prehistoric era, I remember Koshling replying to the OP/team member that one cannot make things which a big impact on the game modular, while the following reaction of the OP only considered the mechanical aspect without any reference to modularity in the sense of its effects on gameplay or AI. Whether or not Koshling actually meant that mechanical aspect is not really the point here (though given Koshlings dealings with AI, I personally strongly think he didn't), but the reply suggests something about the way which the OP approaches the adding of a new game-aspect.
I'm not in a position to tell the team how to work on their mod of course, but I can imagine how its current decentralized laissez-faire civic invites both innovation (good) and imbalance+AI weakness (bad). Which indeed has resulted in a current game on my harddisk with awesome mechanics and more novelties added every day, but an AI which gets more and more crippled every day since it can't deal with them properly and balance suffering from 'collateral damage'. If some dork (like me, in this case) playing without much skill or any strategy, without checking his leaders traits until midgame and playing on deity before the middle ages already feels like he's won, it testifies to that assertion of the AI having a hard time to cope with all the changes. And it's not an incidental fluke- at least since october there hasn't been a C2C game I didn't abandon between ancient and middle age-era due to having technically won with no remaining threats, and several other posters including Koshling himself mentioned the same issue of the game being not much of a challenge. Without downplaying Koshlings AI programming efforts by the way. With lots of commercial games programmed by paid, professional and full-time people still suffering from crappy AI, it seems a tad optimistic to keep adding new stuff and trust both balance and how the AI has to deal with it will be sorted out in a satisfying way later when the addition is already a fait accompli. Can the team please, please, pretty please with cherry on top consider redirecting their efforts to making the game deal better with the added stuff, instead of adding even more stuff? The doctrine of "more being better" doesn't automatically seem to apply anymore, and it even starts to be counterproductive. No matter how much neat mechanics are added, if a player gets his victory on a gold platter by just sitting, building and waiting it's not much of a mod which adds fun to the vanilla game. Since this is exactly how C2C now plays: a gold-plated automobile which has built-in whiskeydispensers, tastes like pizza when you lick the dashboard and has a set of great tits to rest your head against - a man's wet dream, if only the designer had thought of adding a proper engine as well.
A problem which Zeinul recently addressed: there is too much gold. Currently I'm playing a Deity game, and though I started outteched big time I could just buy my way up the tech tree as soon as I shared a religion with one of the techleaders and did some sucking up. Gold had become a more or less irrelevant factor - what's a mere 2000-3000 gold for a key tech when you have over 30.000 (and more coins keep flowing into your coffers)? And after having bought your way to the top, it's easy to modernize your own civ and become the powerhouse of your age. No fancy leader (played Hittites - I think its leader is expansionist/imperialistic while I'm a builder rather than a warmonger) or a sound plan of action other than building as much stuff in my cities as possible and keeping research at 100%. Which is not much of an impressive or coherent strategy, I guess.
Even though my gameplay sucked, the game nonetheless handed out enough cash to break core game aspects like keeping up with tech. But also aspects like crime (the extra costs for watchmen are irrelevant), many events (the costs to do anything, like rebuilding a burned down forest or building, are peanuts in comparison to income), the choice whether to upgrade obsolete units or not (with lots of cash it's close to a no-brainer, effectively eliminating the choice) and the building of wonders (if others get close to building a wonder I'm working on, I just shrug and finish it by paying) are heavily affected by more or less money. Of course one can solve that money-issue by either reducing the amount of gold handed out or by approaching the problem from the other direction and modify the costs of things - make all costs depend on the amount of in-game money, for example.
But maybe it's useful to step back and look at the bigger designing picture. Its clear that in civ4 every change to the game affects a lot of other aspects. Instead of that cash-issue, one can make a similar list of effects as the one above for mechanics like hunting, rogues or the caravans-which-can-be-converted-to-hammers. When reading the posts of the modding team on the forum, lots of enthousiasm to add more and more stuff is shown, and the following decision of whether to add it or not seems to be purely decided by the mechanical feasibility of implementing the idea and the personal vision of the one programming that idea. The issue of having to keep the game as a total balanced and challenging seems to be becoming an afterthought rather than a central consideration. In one of the "fresh idea"-threads regarding some new mechanic for prehistoric era, I remember Koshling replying to the OP/team member that one cannot make things which a big impact on the game modular, while the following reaction of the OP only considered the mechanical aspect without any reference to modularity in the sense of its effects on gameplay or AI. Whether or not Koshling actually meant that mechanical aspect is not really the point here (though given Koshlings dealings with AI, I personally strongly think he didn't), but the reply suggests something about the way which the OP approaches the adding of a new game-aspect.
I'm not in a position to tell the team how to work on their mod of course, but I can imagine how its current decentralized laissez-faire civic invites both innovation (good) and imbalance+AI weakness (bad). Which indeed has resulted in a current game on my harddisk with awesome mechanics and more novelties added every day, but an AI which gets more and more crippled every day since it can't deal with them properly and balance suffering from 'collateral damage'. If some dork (like me, in this case) playing without much skill or any strategy, without checking his leaders traits until midgame and playing on deity before the middle ages already feels like he's won, it testifies to that assertion of the AI having a hard time to cope with all the changes. And it's not an incidental fluke- at least since october there hasn't been a C2C game I didn't abandon between ancient and middle age-era due to having technically won with no remaining threats, and several other posters including Koshling himself mentioned the same issue of the game being not much of a challenge. Without downplaying Koshlings AI programming efforts by the way. With lots of commercial games programmed by paid, professional and full-time people still suffering from crappy AI, it seems a tad optimistic to keep adding new stuff and trust both balance and how the AI has to deal with it will be sorted out in a satisfying way later when the addition is already a fait accompli. Can the team please, please, pretty please with cherry on top consider redirecting their efforts to making the game deal better with the added stuff, instead of adding even more stuff? The doctrine of "more being better" doesn't automatically seem to apply anymore, and it even starts to be counterproductive. No matter how much neat mechanics are added, if a player gets his victory on a gold platter by just sitting, building and waiting it's not much of a mod which adds fun to the vanilla game. Since this is exactly how C2C now plays: a gold-plated automobile which has built-in whiskeydispensers, tastes like pizza when you lick the dashboard and has a set of great tits to rest your head against - a man's wet dream, if only the designer had thought of adding a proper engine as well.