What about having all those uninhabitable planets searchable for loot? There are so many in the game and it should be easy enough to implement. I was thinking maybe you could find precursor or even crashed rival faction ships. You could add risk by having some planets as traps where you get attacked by various difficulty aliens, robots when these planets are explored. Some other things you could find would be long lost treasure such as  bc credits or even tech, unique or otherwise, and even components that you could combine or trade with other factions to assemble ships, weapons etc.

Another idea I had was maybe introducing a space casino where you could gamble your bc credits away just to break up the game a bit when you just want to take a timeout from the exploring, conquering etc.

Lastly, how about an auction system implemented ala M.U.L.E (Old game that I played on C64, yes I am that old) where you can trade with and vs other factions for tech, materials, ships, planets etc. This would make the economy a more dynamic place. I found the tech trading was too easily abused in previous Galciv games. Maybe you could use an auction system to remedy this problem somewhat. Thanks for listening to my weird and wacky takes on this game.