The one time we've tried, the Super Scenario, is very playable. Correction: the EFZI scenario was also a City-terrain scenario and it worked well enough to get the Mod of the Decade award. I've had a peek at Vuldacon's almost-finished EFZI sequel; it's unbelievable.
I wouldn't worry about that: most historic war mods start with large numbers of units to move, including the WWII in the Pacific conquest scenario that comes with C3C (and sets the AI -the Japanese - to attack on the first turn!). Don't forget that some guys were moving little metal units around on tabletop battlegrounds long before computer games came along.
Such a "battle" scenario, done carefully and accurately (with great graphics!) could be fascinating and educational to make, and interesting to play, I'm sure. It could be a good multi-player scenario, too.
Thats so funny you should talk about the little metal units. Jeffery has such like you talk about. (He's very careful about anyone touching the map


In such a mod, your larger city would be very handy indeed, because cities would occupy several hexes.