Here's an idea that would change how the military side of civ functions:
Treat food in the same way that gold is treated.
Units costing food. production, and/or happiness was taken out between Civ 2 and Civ 3 and presumably the designers had a good reason for it; I would be happy to see it back in, but not with an empire-wide food pot - that steps way too far away from city management towards whole-empire-level management. I would rather have units have home cities, which they cost food and shields and maybe happiness, and cost money at a whole-empire level.
This would put a soft limit on number of military units--a limit that one could stretch through certain types of city development and strategy. And it would have very little micromanagement---actually, less than is the case already, because food would not have to be managed at each individual city.
Not everyone considers reducing micromamangement a good thing.