I think SP would get even better with these ideas;

More options for weaponry: Adding weapons such as nuclear weapons, cannons, variety of different bombs and missiles, and more would make this game more fun for those who'd like to venture into military vehicles like bombers, fighters, tanks, APV's, etc.

More ways to propel: Wheels, jets and aircraft props are cool, but we need a bit more. Maybe water propellers, tracks, yup you get what I mean.

As for more ideas, maybe armor plates to temporarily deflect damage, submersibles, computer block to put in structures that when activated they move on their own, it can go on. Please pitch in on the comments.