My group and I love the spell books, but we store all non-used cards in a binder with card holders, and call it the book of infinite spells!  We talked about eventually may need to separate the spells by type, so may have a few binders towards the end. For us, that does not seem that bad, but we have shelves loaded of all types of games and table top miniatures.

IF not including the spell books DOES NOT decrease the price for the expansion, then continue including them in the expansion. If you do not want them, there is always eBay.