I think a good book project would be along the lines of the Genesis "Chapter and Verse". Chronicle the entire Beach Boys story by interviewing the remaining members and the people that have been associated over the years with them and have them each give their own perspective over different issues. Only use text from the transcripts themselves without an author giving his own interpretations. By telling the story in their own words, overall there would be a balanced view from each party.
U2 did a book like that. It was quite good considering it was all transcript. Though, It seems to me the guys were all in the same room at the time of the 'interviews' and thus the book read very easily (like reading a conversation). Whereas I can imagine the Beach Boys book to be disjointed and confusing (hearing Mike's interpretation of the SMiLE era, then reading something completely different from Brian's point of view). Plus, Brian is known to be a little off kilter when it comes to giving answers.
I love the idea though. Also, to add to to
filledaplage's good idea, add a musical and historical timeline at the beginning of each chapter to set the mood of the era.