You can use one 4096 texture with sixty-four 512 book covers or two hundred and fifty-six 256 book covers (!) on it, which reduces the number of materials. A couple of those materials would cover a lot of books.
What, specifically, is your concern? Performance? If you bake all the geometry and lighting, and don’t make books movable, you can probably get very good performance out of such a scene. If each book is movable – that probably will be less smooth (even if you don’t physically simulate all the books.)