I actually find the old books to be very useful. This game doesn't quite tell you the story in a straight-into-your-face manner, so looking up the details via other means was necessary to understand the story. Especially those books detailing the manhunt incident and rune cannons. The fact that this game doesn't have any other game to rely on (and compared to the others who already have millions of side publications associated with them), these little hints helped a lot.
The only problem though, most of these books are gotten via very mundane tasks. Like those mini-games. If only they were not that tedious, I would have enjoyed it more.
Speaking of the contents of the Old Books, I believe there's an entire FAQ on GameFAQs listing all of them. Check it out.