I think it's more that people are responding to your "I just have to resign to the fact that I'm beyond this game's challenges" with helpful suggestions as to how you can continue to find fun challenges to overcome. As far as part mods go, I think it's kind of hard to give recommendations because installing mods is all about customizing the game to your own individual needs. I can tell you what mods *I* use but that doesn't mean they'll be the right ones for *you*. However, if you're concerned that you've run out of things in the game to do, just installing more parts might not be the answer -- you seem motivated by challenge, and just flying to places you've already visited in different-looking spacecraft might not be enough to keep your interest for long. You might be better served by gameplay-altering mods that add complexity and require more careful planning (things like TAC Life Support or RemoteTech), give you a long-term goal to work towards (like getting a completely self-sufficient colony running in MKS/OKS), or just straight-up increase the difficulty (Better Than Starting Manned).