Dun dun duuuuunn!
Yeah, okay that wasn't quite as funny as I thought it was going to be. Here's a thought. What if you didn't have to manually rename your units after receiving an upgrade?
I sometimes find myself thinking, you know, is this older unit here as good as this newer unit here? Without basically lining them up side by side to compare their stats, I just don't know. But if there were subtle hints in the unit name then that might help. Particularly if they have a trait that scales with level. If I'm making cutbacks on troops I don't want to disband a unit that has their level as a modifier to Dodge, that would be insane. 
If not as an option for the actual game, at least open it up for the modders to have a crack at it.