Jaded spacer here, any mod suggestions?

[Material Defender]

So I just cracked the 400 hour mark, and by this time I've done most everything. I've got stations around and bases on every orbital body. If a kerbal can get to orbit, say with any one of my basic SSTO designs, they can interact with my network of large and small interplanetary shuttles and landers to go to and from any planet or moon in the system at minimal fuel cost (not that ample fuel is a problem, each station has massive surplus). Bill, Bob, and Jeb just had a reunion on the surface of Eeloo, each coming from somewhere different in the system, just for kicks.

But now I'm, astonishingly, running out of steam. I need a new challenge. What would be your recommendations for mods to inject some new fun in my game? I've been playing full vanilla and never really felt a lack of anything in particular, but now I want to know - are there any mods that you felt really enhance your KSP experience? That would be a good way for an old spacer to feel a little bit of that excitement again?

[Talisar]

Realism Overhaul if you want to turn it to 11