Potent Staff: If your spellbook staff does not have a Spell Attack bonus from a pre-existing enchantment, it is now treated as having a +1. At level 20, this benefit improves so that if your spellbook staff does not already provide a Spell Attack bonus of at least +2, it is now treating as having a +2 to Spell Attack.

So a struggle on this particular skill. If you are a wizard who has gotten a staff with a + to spell attack, this entire ability becomes completely worthless.