I had the opposite experience: Infinifactory was great because even my kludgiest creations got to the point of giving a warm fuzzy "I made dis!" emotional payout... which is what drove my interest in optimizing against friends.

In contrast, some of the less-friendly (and less-intuitive) limits in the "boss battles" of SpaceChem simply turned into big painful dead-ends, leading to me abandoning the game on the final level. (And swearing I'd get back to it... someday.)

I think the distinction speaks a little bit to the spectrum between "problem solving" and "puzzle solving". Both games are solidly in the former camp, but Infinifactory feels far more like a creative unique exercise.

Plus, I kind of need more of the life-lesson: Getting something "ugly" that works and then iterating is better than holding yourself to an emotionally-safe but difficult standard that keeps you from getting work done :P