I'm at Sol 250-300 right now and most of my time has been spent creating new domes for people to live in and creating work for them to do. I've unlocked pretty much all of the wonders/research and I'm waiting for my last Earthborn colonist to die before my colony becomes 100% Martianborn (not sure if this is an actual achievement or anything, but it was a personal goal of mine). I completed my Mystery (Metatron) which was pretty great considering I was still "testing" myself to see how far I could last on this playthrough. I'm managing resources pretty well, money isn't an issue, and I'm fairly comfortable I can keep this going as long as I keep up with food and housing demands (I refuse to enable birth controls just for the added challenge).

Does anyone else ever just start over to relive some of the early game struggles, or am I just a masochist?

It's also worth mentioning that I only have the base game right now. Should I just start a new game for a different mystery? Should I look into buying one of the expansions, or maybe look into some mods to make the game more interesting? What do you usually do at this point?