I don't see the problem with getting an album with tracks that are already released, look at all the other genres in the world. An album should not be about releasing "9 fresh unreleased tracks ready to bomb the dancefloor!", but about what tracks really represent the artist.
For instance, I would like an album with Fungus Funks tracks for 2003 and 2004, on one disc, instead of having to change cds all the time, from compilation to compilaiton.