You've already put wizards in a good spot for a multitude of reasons:
->The implementation of a variety of different classes, Beguiler, Warmage, Hexblade ~ and other alternative classes like Voodan. You've increased the diaspora of potential casting classes beyond the pre-Enhanced Edition days of just the duopoly of Wiz/Sorc. I have to imagine there are far less wizards rolled with the multitude of options since spellcasting and high magic options in general are more diverse.
->The implementation of new crafting materials, offering incredible save vs spells should you find enough of them and proceed to slot them all, even some offering straight up immunity to what was the most complained about spell, with simply 1 ingot in your boots.
-> Nerfs to many spells over a long period of time, Fog stacking, Time Stop, IGMS. These were necessary adjustments, but the psychological impact on some seems to persist.
-> The substantial nerfing to Wizard related drop items. They have been nerfed into oblivion to the point where they are vendor trash. The robes are awful now, and the rings are more common than most would come to terms with. Every Wizard related item I have ever seen has been nerfed into absolute commonality.
However, the book is a cool idea.
I see it working a couple of ways, if you really wanted to put Wizards into post World War II Germany status.
-> You implement the physical spellbook that can be taken, but a wizard should have multiple spellbooks. They would be scroll based, and you would buy the scrolls and load them into the book. You don't simply forget spells, you just prepare them. Its the only weakness a Wizard has is their own lack of prep.
-> Spellbooks could be augmented. Theres a weak, traveling spellbook that is meager at best (The most common one of reference), There should be then, enchant-able holdable spellbooks that offer even greater spell slots that could potentially be disarmed.
-> A Wizard can cast spells without their book, if they have the scroll in their inventory.
->You can give your spellbook to someone who has high UMD, and they can cast everything from it if they can read the scroll and pass the UMD check.
Ultimately, big dev task. Fun to think about.