That’s a completely valid use of XSPF. It takes great advantage of the semantics, and I like it a lot.

Something like this would make the statement that the URLs in the location elements (“locators”) are equivalent, and the URL in the identifier element is a name for the abstract song which both locators are pointing to specific instantiations of:
playlist
 tracklist
  track
   identifier
    http://en.wikipedia.org/wiki/Purple_Haze
   location
    http://example.com/one-version.mp3
   location
    http://example.com/another-version.mp3