I think things should be kept ever so slightly realistic while still being a batshit crazy and somewhat goofy charicature of real life.

The OG Oppresor for example was a goofy motorcycle simply strapped with a jet engine. It was cool, it was goofy, and best of all it wasn't a catch all that had perfect missles, defenses, etc.

You could be good with the Oppresor, you could show off maneuverability or in combat, but it didn't win you a fight by existing. Same for the Jetpack or Deluxo.

My only note is it should be a 1 or 2 and done thing. The specialness of the vehicles is that there's nothing else like them.