Absolutely for the multiplayer.
The game evokes memories of some games: Dungeon Keeper (the underground digging part I suppose),
I don't know if you've ever seen that program/algorythm called "game of life". It's maybe a bit to far but have mecanics of self replicating structures could be interesting. For different purpose as explore, fight, replicate and so on.
You got it for the abandonned bases! Sounds funny and rewarding :)
For the bosses, depending on the story/universe you could have some big creatures (or other structures) trying to grab your precious ressources. Imagine those creatures attracted by light or electricity. They'll go away with a few hit first but they'll come more confident. Then they could if defeated give you the reward with those same blueprints.
One interesting thing with your ressource management is that if you have some limited core energy, you'll be forced to make choices (could be tough ones) to dismount some old constructions to build somewhere else. It could lead with some weak points in the structure where you should pay attention. Or try to grow like the enveloppe of a cell :)