You are using them with prophecy monsters right?
Well, spellbooks work co-inside with the the prophecy monster, with their effect either causing you to bring spellbooks back into your hand or discard it to be activate a good effect(for example, strength of prophecy likes to return spellbooks to the deck). Kinda works in a loop, so you could be doing the same steps every turn.
Only Prophecy that doesn't work with my "discard or return to hand" theory is high priest of prophecy, which involves banishing spellbooks. However spellbook of alma helps support high priest's effect as it allows you to return banished spellbooks back into your hand.
Finally, Justice of Prophecy and temperance of prophecy allows you to get a level 5 or above spellcaster from your deck, adding it either to your hand (justice) or actually to the field (temperance). so this allows you to summon either high priest of prophecy or in my case, a dark magician.
So overall, best to use it in a deck with lots of prophecy monsters and the odd spellcasters.
Spellbook is actually one of my most consistent deck