I'll have to go check out some caves then. The world is so nice I'm enjoying running around on the surface though. I don't mind a bit of cat and mouse with the Sentinels really, keeps it interesting.
As far as leaving goes I don't mind the dynamic. I know I'll be sorry to say goodbye to this world, but I think that's part of the concept of travelling - moving on. Also, it would be pretty easy make tons of money if you could just keep going back to the rich planets. I think having that choice to stay or leave is an interesting part of the game.