Cool idea! I do sort of wish that you could upgrade the tower in-between rounds and that you could direct the guys to fight a specific enemy, it's kind of frustrating when you've got one bashing your tower and they're all fighting other things.
I concur with the second point, Right now the strategy is to have stuff saved up to counter people who get through defenses. They always target the closest matching enemy and someone coming out of the tower's closest enemy will be the one of that color. It's not a perfect solution however.
