However, you can have iTunes download album art (even for albums you've imported and haven't bought through iTunes) for free. You can just select every song in your library and the right-click and choose "Get Album Artwork" or something like that. It works decently for music you have somewhat accurately tagged (at least a correct artist and album name). Again, this fails for a lot of electronic music though.
EDIT:
Yeah, see the guy he replied to. He's referring to Spotify Premium.
It also fails for classical music. But since I ripped CD's I just scanned in the cover and added the art. Trust me, it was time consuming. But there is hope, iTunes has added much more classical/opera recently. So changes are, if I had to do this all over - a lot of the art would be available from iTunes.
I would have no problem paying double that each month for Spotify, and upwards of 3-5 times that if it had a music catalogue and organisation structure similar to iTunes. Granted, I value music more than many people, but $10 is what a cheap lunch costs, for unlimited music on demand.
Find artist Download/buy albums Listen to songs, rate, put in playlists Sync to devices (this it solved)
In terms of your issue with iTunes cover art, didn't they announce some thing where you pay a flat fee and is basically matches all of your illegal music with legal one when iCloud was introduced (I never tried it just remember the keynote vaguely)