Armies:
I'm not sure, but I think if you play at a higher difficulty level, the AI will use units in larger numbers to (i.e. bigger SoD).
I've found that when you're making an assault into enemy territory--with or without an Army--the AI tends to resign its units to cities, thus you're able to go about pillaging everything anyway and inevitably have to resign yourself to sieges using artillery to batter down the dozens of units stacked in the enemy cities...even though the enemy may even have a numerical advantage and could easily engage your units the moment they cross the border (meaning the AI 'knows' you're there).
The biggest problem I find with Armies is that the AI will simply not build them often enough:
I've even given them free Armies and nothing. They just refuse to load any of their units into the Army, even when they have plenty of units with Attack role (assuming the AI were to only load units into Armies where there is a surplus of units proportional to the number of cities).
New request:
Stealth Attack via Bombardment
I know this feature is designed for use by the attack factor but the fact is that air-to-ground combat is really where this best applies; air units attack from above therefore have the luxury of attacking any target on the ground--there is no way of defending weak targets if there are no AA units present.
That's the strategy--everything from Stukas dive-bombing T-34s to modern precison-guided missiles and drop-bombs destroying specific targets in groups on the ground with pin-point accuracy.
In short, air units have to be able to select units in a stack for bombardment. I know this would deviate from the standard interface but it's a popular--and logical--idea and shoudl be considered.
Similar Request:
Air Units can Target Specific City Improvements
Pretty much the same arguement as above, only in this case it's about strategic bombing of infrastructure--preventing the enemy from effectively making war in the first place. Another major strategy.
An interesting plus could be that units without Precision Bombing flag checked, may occasionally hit a different improvement, population, unit or miss altogether.
I figure that this somewhat exceeds 'simple modifications' but I figure I might as well put it on the table.
[Oh and again, do consider the 'Raze' flag mentioned earlier. It's rather important from us modders.

]