Do I understand you correctly in that you attribute increased power usage to the intricacies of copyright law (at least in part)? Because that's an interesting angle that I hadn't even considered yet. :)
Well, I opened up my supposed music cache from Spotify once and u dont get a list with audio tracks, but encrypted data. The cache was about 12gb large so it must be the audio.
If it was the pure audio source then nothing stops me from copying it and put it in my own library, possibly shared with anyone through my own NAS avoiding ads and future subscriptions.
I could also just stream the cached folder into my own app, and while losing the ability to pick songs in real time it effectively becomes a radio given the main client keeps running, which I would do on a random cheap pi or server.