What I want to know is what happens if you click "upgrade" but the song you want to upgrade is not in your library at present. I lost a few of the albums in my purchase history.. it lists 212 total songs, but 57 songs 11 albums underneath that and there are 57 songs on the song list.. but it wants to charge me $47.95 to upgrade.. when if it is only including the songs listed, it would be $17 and change..
If upgrading my library would help me recover my lost music, then yes, I would do it.. otherwise I'm not interested in a bulk upgrade.