I'd buy that book
The Onion AV Club has excerpts from the extensive liner notes Elvis Costello wrote for the recent reissues of his albums (of which I own The Year's Model and wouldn't mind a few more if they didn't cost so much). They mention that if you put them all together you get "the equivalent of a 100-page autobiography". I kind of wish Costello would get them all together and fill in the gaps and release that, actually.
