Another idea for expansion. In the same way that there are one-time-use caves, you could have some one-time-use rest sites or rest sites that can be used once every x hours/days. This is assuming that you haven't planned to add a rest site elsewhere. You could also have randomly appearing bonuses, requiring players to check Expansion frequently. These could be rest sites or even just randomly appearing Creds, Expi, Equipment, Eggs, Orbs etc.
Maybe add the tree that I suggested for Sanctum as a building in Expansion. This could cause these random bonuses to appear.
I think it might be an idea if the caves can be accessed every x hours/days as there is virtually nothing to do in Expansion. Having them be destroyed after one fight seems like a bit of a waste of a feature.