Do that stay on earth or do they fly in spaceships too? If they can drive spaceships then try adding more ships like maybe one that’s faster but has less health or one that has lots of health but has bad laser blasters.
If you need some more ship design ideas then I’d recommend reading Skyward by Brandon Sanderson, it’s really good. Just don’t copy it, you’d get banned for copyright.
For the parts where they are on earth or in a space station maybe let them get different weapons like a machine gun or a sniper rifle, they could also get abilities or armor like in Metroid where there are tons of cool things to unlock. Once again though, don’t copy Metroid or Skyward.