This brings a good question: What means "level-up" other than something about rules mechanics?
To me, it means better understanding, comprehension and practice.
You may find a book with tons of spells in it, you still need to practice. A spell is not just "a spell" that can be cast with saying a magical formula.
It is manipulating mana/ arcane magic essence and it needs practice to understand how it works. So for you PC who finds a book I would suggest him to ask him to decipher some part of it, to understand the meaning and then actually access the spell. He'll spend some in-game time to do it and hopefully reach the next level by the time he gets the spell.
He can practice, of course. Then you may allow him to try to cast it with a fumble range 10 times bigger, until he levels-up or add funny effects, for the scenario advantage (or not).
That's exactly the same with skills. What if a player spend 1 month on a ship to go from A to B. Is this time wasted? For me, he can practice and gain temporary development point until he reaches the next level. But never, the DP are given for free. It would be too easy.
I believe learning process should be harder (spells and skills) but because it is a game, rules allow to level-up quickly.