I have another one. The different civs in areas have different languages and they would work like religions. The can spread and you can choose what your language is. Anyway there is a national wonder called "(Insert Language here) Language School" and it would improve you relations with civs with that language or something like that.
I don't know if it's already been considered or added, but how about the fossil fuel and non-renewable resources gradually disappear after use? Since Oil is going to run out completely by about 2050, coal and natural gas some time after that, we do need to consider a world in which it simply isn't present.
Civilisations will have to advance sufficiently to exploit crops and land to make replacement resources (perhaps the resource becomes available after the technology is researched) before their economy and military simply die out..
Cold Fusion is already in our game as one of the most futuristic techs, we could set it so once you get that, you don't need any resource to power vehicles. I don't like the idea of having a new resource appear, so much as using technology to get rid of the dependence on resources, which is what is most likely going to happen in reality (in a long, long time).
population of food? do you mean stockpiles?
sounds rather AofE to me here...