If you do manage to delete everything, I'd be interested in knowing what develops afterwards.
I feel like I can relate in a way, though. I've downloaded so much over the years, for a plethora of reasons, but mostly just because I could. I've spent an insane amount of time 'perfecting' my digital music library (especially the Japanese stuff), as if I were rearing it for some kind of grand exhibition in a future that hasn't come. But at the end of the day, it's much less of a spectacle and more like a cesspool of unbridled self-indulgence.
It really brings to light how much of a double-edged sword that downloading music can be. For me it started off as more of a childish fascination, but these days, I feel like rampant, poke'mon music collecting is just unnecessarily bombastic and even a bit perverse. When I first jumped into the deep end of piracy, I hadn't considered the possibility that I'd come to value something as immeasurably fulfilling as music in mere megabytes. I guess after years of lacking self-moderation, I've finally had my fill.
And with that said, I've been trying to cut back on this habit. I'm also making an attempt prune my library of all of my whims and passing-curiosities. It's a tall order, considering the stack of shit I've piled up for over a decade now, but ideally, I'll get my library back to things essential to my interests.
CD/Record collecting is probably a more worthwhile endeavor, though. At least it's something that can be passed on to future generations, and is a bit more tangible than readily perishable digital files.
I feel you on last.fm btw. I never stopped scrobbling, but...that aesthetic experience you mentioned is almost non-existent now. Any traces of it are buried deep under the poor design and alleged functionality. Still, I wouldn't blame you for returning. Hell, I didn't even have the balls to leave the damn site.