In the long run it may pay off. I'm going to try to like in Medieval Total War, destroy every building that they've built, and kill off the populace. That means, that if I can demolish the buildings, and without the populace, they wont be able to make any new units, only the outdated units that suck! Also they wont be able to upgrade their cities any time soon from the horrible population losses. So once I kill off their good units, then they'll be sending sucky ones, and my battle hardened units will mow them down, giving us a wonderful path to the Romans end.