Blumofia: If the bug was on a skyscraper especially, yeah, you are not going to do much damage. building are very good defensively; with all of the testing I've done via the games I played it became very obvious that was the case. Definitely target zombie units that stray from their protection, and use it to your utmost advantage. Sheep also only have a ROF of 5, that is part of it too. ROF is a very important factor for all the bombard units.
Edit: Oh, and I think you are a dead man, no offense. If it is Day 5 and the bugs are here, you will soon not be. It usually isn't until the bugs show up, that the AI starts to lose cities to the Zombies. Then things fall apart....
Vuldacon: From all of the games I've played so far, I honestly don't think razing is very much of an issue. I've seen a FEW buildings razed, but even when I and the zombies exchanged the garage over and over for a few turns, they did not raze it. Besides, that's what zombies DO, let them have their fun!
I think you have the right idea about the maintanence costs, so go ahead with what you plan for it now. In my experience, the only faction with real money issues is the Authorities, probably because of all the corruption from being so spread out and far from their capitol. The Farmers likewise could develop some problems with cash maybe, but I still think it is doable there. Survivors and especially the company have no real money issues(except of course you could always use a little more!). What the Farmers do need, is an advanced government later in the game. Something to kill WW and maybe a bit better corruption, that's the ticket.
What DOES concern me, is the unhappiness problems I had in every game. I was running like 40% luxuries in almost every game, and still having some problems! Getting certain key wonders/buildings really helps with that, and the better governments. I am not certain if it is an actual problem that needs to be fixed, but you might wish to review it/get other opinions. Note also, that even with running 40% lux, and doing mostly enough researach to get minimum tech times, I had few money problems, as I mentioned above.
Corruption and War Weariness are the two big hurdles, from what I've seen. Any time I was able to improve either of those elements I got a big shot in the arm, production/money-wise. I want to reiterate that I was wrong about the bank-type minor wonders; they are VERY important. This last Survivors game on Banned alone, the only thing keeping me in the green at all was the interest from building the Auto Shop.
I think mostly things are very well balanced, but I don't personally like running out of tech to research a 1/4 of the way through the scenario. But maybe that really is asking for too much. Might you take a look at using longer minimum tech research times? I really think that is called for myself, let's hear what others think. Something on the order of 10-15 turns, I am thinking. There is usually some tech trading going on as well, at least for the common techs; that's part of it.
I'm kind of scared of what you have hinted of for the next version myself. The game is already quite nasty; when the Monsters show up, things get very,very hard. When the bugs start showing up, it gets hairy, even if you are 'winning' at that point. Anything worse then that is going to be sheer hell to deal with, on any level. The game does not really seem to be THAT much harder per the difficulty levels, mainly because everything is already preset. In playing lots of scenarios with everything already going from the start, I find that is almost always the case.