Colonization had a very good management resources system. I think that this will be optimal for Civ IV. You could produce the different resources in quantities that could be stored or sent to where they are needed. This (and it is practical, as it has been done) will add realism, and create industrial regions where maybe they do not have resources, but have the industries, other countries or regions maybe have the resouces but not the industries to manufacture them. Also will better the trade system, because you can sell given quatities to different civs at different prices, also private merchants could be added that will buy for example iron from you, and the sell them to the people you are at war with. That will also increase the importance of the comunications systems, that for the time being are more important for war than for the economy, but in this way, they will be crucial for it, imagine that you only have a coastal city, and there is no wood to build ships, then it will be key to build a city near a forest and build a road to transport the timber to the shipyard, if this road is destroyed or taken by your enemies, the only wood you will be able to use to build your fleet will be the one you stored (if you did). Anyway, I think that the economic, and population especialization and education, trade and resources systems of Colonization will improve CIV 
IV.
IV.
