With a 2 person ship you could have co-pilot perform the extra weapon points 1 can't access due to 2 buttons at an instance.
With 2 persons you could add STEAL THAT SHIP for pirate roles. - once you convince an NPC to give up and escape pod you could board it for 2nd player to steal and do whatever you want, sell or keep etc.
You could get 1 player to guard a zone for your floating cargo which you are managing to trade whilst you go searching good places to sell it at (have NPC come in plus other players investigate your USS you created in doing so)
Ferry all your ships around to same locations.
Tons to add...