They stream in 320 for premium users and don't use P2P any more. Sources:
p2p program was shut down: http://techcrunch.com/2014/04/17/spotify-removes-peer-to-peer-technology-from-its-desktop-client/
Yes. I know that. I'm saying not all the music they stream is in 320 kb/s, which implied I was talking about Premium. I may have been wrong about the P2P (which means they could do CD quality,) but Spotify does not stream that 320 kb/s a 100% of the time, nor have all their music at that level:
http://www.marcurselli.com/2014/03/03/the-truth-about-music-streaming-services-and-the-ultimate-audio-quality-shootout-test-beats-vs-mog-vs-play-music-by-google-vs-rdio-vs-spotify/
http://www.quora.com/Why-is-there-not-much-music-on-Spotify-available-at-320-kbps This one is old, so take it with a grain of salt.
http://www.quora.com/Is-Spotifys-320-kbps-streaming-false-advertising This guy posts a bunch of links, basically saying the same thing: They say they're doing it at ~320 kb/s, but it's not guaranteed. The Spotify website even said at one point, "Not all music streams at 320 kb/s." It's not false advertisement either, since they say it's an approximation.
If this was a couple months ago, Spotify would have clearer superior for the simple fact you could use plugins, 3rd party improvements, and stream your own music from now. Now though? They've closed all third party API off. Not to mention they pay a pathetic amount of money to their artists for each time their song is streamed (I believe it was between .006 and .0084 dollars per stream. Essentially, twenty-one million listens to their track would garner maybe $176,000. You could argue "but that's better than piracy!" But think of it this way, using Taylor Swift as an example: She pulled her music because of this exact reason. She only needs to sell 18,000 physical CDs to make more money than Spotify made her. You could argue "well, she isn't getting all that money back!" Well, she isn't getting it from Spotify either, as she still has to pay her record label and other things that lead to the Spotify sum being paltry money into her pocket.
Tidal costs so much because of two reasons: The servers needed to do lossless music is insane and they're a small company compared to Spotify AND they're paying their artists a lot more per stream than Spotify does. That second reason is the thing JayZ is pushing to get more artists on the service.