The upkeep idea is very good.
However, there should be an easy way to know how much it costs you... Probably the individual cost of each unit should appear in red when we hover a unit.
No, it is absolutely horrible and it makes no sense. Not only that, but it is also very very easy to let a scout wander off too far, an then when you note your economy crashing the scout is too far away to pull him back in time to save your economy. Is this what you see as a good system?
I think it is a bad system, because surely these scouting expeditions become self-supporting after a while. They live from what they gather by hunting, and maybe they can trade for food here and there. The upkeep for these units shouldnot be that steep - at least it should not be a significant portion of your GNP in the early game. That would be nothing short of rediculous.How do you see this in your mind? Does your government ship crates of supplies to the scouts? Does the pay the scouts receive increase just because they are now a bit further away from home?
What makes this idea even worse is that the problem with early exploration is not really the exploring per se, but it is more a problem of the fact that you can give a civ on the other side of the continent a call to traqde techs whenever you please. If you want to make things more realistic - and I do not think that one should want that - then one should abolish the contacting of civs unless certain conditions like creating an embassy are met.
Then there is the issue of map trading that makes the upkeep idea even worse. I do not know about you guys, but in a typical game I uncover a rather large chunk of the landmass by trading maps. That way the exploration phase is over by the time you hit paper, which is around 500AD or so - I think. If you guys want the exploration phase to be longer, one should also adress the map trading since if you abolish early exploring and then allow map trading then the uncovering of the map of the continent will be over by around 500AD - just like it is now. Increasing upkeep does not solve this.
I can go on and on and on on why upkeep is a poor idea to limit exploring, but these are my main gripes with it. One final note before I let the topic rest: How would you handle naval invasions if units far away from the continent suffer a huge upkeep penalty? Would your fleet suffer a huge upkeep as well? Would that not be a huge blow to the economy, to th point where one would be rarely in the position to 'field' a fleet sufficient to go out and conquer? How would this barrier that the upkeep of units that are far away from your borders have a rooting in reality?
What I liked more is the idea of scouting units to be unable to go into forrests - or rather, that units that enter a forrest may get lost and be lost to you, just like triremes in Civ1 had a chance to be lost on sea if they did not end their turn next to a land tile. This way one
could enter a forrest and explore beyong the borders of that forrest, but it would become rather costly, not in terms of unit upkeep but in terms of hammers you need to spend to replace lost units. This way the forrests become a sort of hazard that you may try to overcome, or not. This seems like a much more natural and logical solution to the exploration issue, and one that accomplishes the same thing, that is it makes exploring in the early era's harder, and it would give the explorer unit a niche role if the explorer could enter forrests without any penalty.