> Nowadays, I get Native Instruments Ultimate — and despite sounding orders of magnitude better, all I do is toying around. I always have the nagging feeling there's gotta be one sound or effect in that endless library that's still better than the one I'm using right now.

It may be you're accidentally veering away from "music" into the realm of "sound effects." Many audio software environments too easily lets you drift in that direction. (Although I'd argue that's still better than drifting into the direction of becoming an audio software environment programmer. :)