Some interesting stuff here...
I also love photobooks and have quite a few of them.. 
The ones that I look into most often are Ragnar Axelsson books (Face of the North and Last days of the Arctic), Kenna's Images of a Seventh Day (I wish I could afford more of his books... Lately I am lusting particularly for Le Notre's Gardens, and of course, Japan. But I think I'll have to be modest and just order the two volumes of his Retrospective). Also Fey Godwin's Land and John Sexton's Quiet Light is very nice, his Listen to the Trees is high on my wish list... 
However, as my tastes have changed significantly, I find on my wishlist lots of books about pictorialism - Steichen, Stieglitz and such folks, also some Japanese books... So I started to sell some of my stuff - HCB is already gone, as are the Americans.. The toughest decision that I still haven't made is whether to keep the Bruce Davidson Outside Inside "trilogy" or not.. They are very nicely made books, but the content doesn't move me any more... 
Do you get rid of books that are no longer of interest to you or do you keep them all?