Yeah that's one of the drawbacks of procedural content is that essentially the base gameplay is the same with a different look on each planet. It would have been nice if during the long development they made some different looks for the cave growths like they do for the surface flora. I should continue on my path though, I've spent all my time in the first few systems other than visiting the first Altas Interface and getting my v1 pass.
Shameless plug, but my Adventure's game engine is set to support procedural gameplay, including procedural skills. It's certainly doable (in theory! Haven't completed my game yet) if the gameplay is parameterised up front.
The way I'm thinking of it is encounters. Thinking back among the games I've played, I'm designing around memorable moments and thinking "how can these be parameterised?" Then I can create randomised encounters which, with enough parameter variation, should play differently enough that they aren't samey. But I planned this from the very beginning, and also it screws up precreated levels that makes earlier development tougher. I can set several randomised objectives and targets in a level during procedural creation, but creating these in a level editor isn't easy, and is a problem I've to solve for the fixed-level demo.
In the case of NMS, they could have different gravities and monsters with different behaviour patterns. Each planet could be viewed as an encounter with a specific flavour, so 'fire fight' for one', 'resource management' another, 'stealth' another. Tweak gravity, run speeds (with some science mumbo-jumbo explanation), outposts, critters, etc.
That's something for NMS2 though. I can appreciate what they've doe with NMS as a first title that's dragged on 3 years in the making. Retrofitting some variety, when the idea behind the game wasn't even fleshed out during much of that 3 years, is asking too much. Unless they can patch it in? But I'd say take the profits and go make NMS 2.
