Another idea from that part of my brain that says "IF IT'S REALLY COMPLICATED TO IMPLEMENT, IT MUST BE GOOD!!" I hate it when the rest of my brain agrees, which is often.
Is it even remotely possible to implement some sort of ammunition system for your units? It would increase the realism somewhat, as well as introduce a new tactical element to player decisions. "Do I really want to storm that strong-point with only 10% ammunition?"
Also, it would reduce the leet haxor of certain units. For example, the Pershing, or Panther, or Tiger Ace would only be good as long as it had ammunition remaining.
That means we could also add a new unit! The Ammo Truck!
Yes, okay, it's not going to happen. But a man can dream...