Maybe I am easily entertained when it comes to sandbox building games, but I thought this twist was quite cool.
Here's where I would take it:
Have interesting features on the cliff, like little ledges, small hollows, interesting plants or abandoned structures. Some could be hidden from view at first by the geometry of the cliff.
Lean into a global grid, so pre-existing features can be placed grid-aligned where desired.
Play with the structural side of it, like including some rare, finite elements like beams (player-placed or pre-constructed) that allow an occasional larger area or longer reach away from the cliff. Come up with a way that that matters. If you really wanted to play with it, you could introduce support cables.
Remove repairing as a concept. Structures can be either invulnerable or just die if an enemy attacking it is ignored for too long. Or they could self-repair or something. Repairing is not fun.
Alternatively, maybe enemies could go for key infrastructural elements, which the player has some reason to protect. Repairing would be limited to those.