I think I understand what you're suggesting. I don't think I'd separate out the upgrade points by tank type - just have a single upgrade point total and the player can flick between the 3 different tank types within the upgrade screen and buy powerups for each type individually. Does mean there could be some duplication, but it's an interesting idea.
I'll keep it in mind, but I'm also wary of feature creep!
I just thought about what you said again.
(**)do you mean...
Used on LTank = 5
Used on MTank = 13
Used on HTank = 10
Used = 28
(*)At first I thought you meant...
Earned = 28
Used on LTank = 28
Used on MTank = 28
Used on HTank = 28
but then It'd be too easy, was I thinking the wrong idea when I thought (*)?