I just found out last weekend that the loss of attacks isn't as bad as I'd thought. Tanks, despite the docs saying they can attack multiple times per round, can only do so if the first attack allows the unit to move into the defender's square afterward. If your tank attacks a pair of warriors, it'll kill the first, and then lose the rest of its movement.
If you want to save production costs for units, build lots of artillery, plus enough attack units to run two full waves. Use artillery to soften everything down to 1 hit point, then use attack units to finish them off. Never use an attack unit that's not at full strength. As soon as it takes damage, move it back to a barracks city for repairs.
For quite a while, I was fighting an enemy that had the goods on me tech-wise. She (Cleo) had tanks and mech infantry; I had infantry, cavalry, and artillery. She took many more losses than I did, because she kept trying to pound my full-strength infantry with her tanks, while my infantry and/or cavalry only attacked after my artillery had weakened them. It took a while, but I finally wore her down, and in the meantime I never lost a city.
Meanwhile, perhaps the best use for an army is as a city-cracker. Use it to bust that fortified mech infantry in the size-18 city across the river. Armies are also good to stick in a town you've just taken, to repel the counterattack. Oddly, unless your army has very weak units relative to it, the AI will almost never consider trying to take it on.
