Between Discogs and YouTube, I am having no trouble discovering and acquiring high quality content that can be used arbitrarily. For a period of time, I thought that old-school CDs were actually dead. Today, I get regular emails from la-la land records about incredibly esoteric 90s cartoon soundtracks that I can purchase new. I believe that there has never been a better time to get into physical media. I've got a lot of stuff on hand that you cannot listen to on Spotify. You won't even find some of these artists or "labels" in there.
Spotify also puts me in a really bad mood when they decide certain content is no longer permitted for playback. Every time this happens I spend about 3 hours ripping my most recently-favorited tracks via audio driver trickery, just in case it happens again.
The only value proposition for me is that their app is ubiquitous and can be controlled from any device. If I could find something similar to the Spotify application experience that I could point at my own backend, I think I might go for it.
And, I totally get the other target audience: People who just want some mindless background music or podcast while they drive or do cardio. Spotify is amazing at this, but it's not really a big selling point for me. Definitely not enough value for me to pay a monthly subscription fee.