Okay, before the High Lord of Munchkinry here gets too carried away, I might just clarify a few things.
The five books you've found are five basic books on magic - Water, Fire, Force, Light and Earth. They are meant to help mages who can't project magic to learn the basics of doing so. Which is why it bumped Ekoka up to level one, but Thuun just learned a new spell. Each book also has some generalities, such as other applications for the fields. Non-mages can't always find useful things, but if Felice was of a mind to learn psychic abilities then he might find something useful.
Your best chance for selling the books, if you so desire, is in a big town. As you might remember even larger towns currently don't like mages very much on account of suspicions vis a vis cutting the damn sun in half, but at least larger towns should be less suspicious. You can hope.
"Wait, I've only got the water and force book here. Which one of you took my fucking light magic book, I was going to read that one! In fact I distinctly remeber having 5 of these damn things, you bastards better return them, because I was planning on selling them to buy more arrows and a new bow."
You only had four books. The fifth one was found by Ekoka and it's all his.
((OMG, this has provided SOOOO much material for my mad min/maxing. I mean, for one thing I'm possessed by the ANGEL OF CREATIVITY, which I read as the Lord Almighty of Munchkinry. So I imagine keeping him happy will mostly involve "do what you been doing, you crazy motherfucker" and probably also "don't be a dick" which my negative trait kinda weans me away from anyway.
On top of that, the revelations about Light magic are pretty awesome, and mean I now theoretically have a bonus to YOURSOULISMINE and the Pokémon summons that I will probably find flimsy justification for at some point.
So yeah, just the lore and understanding granted by that ALONE compel me to READ ALL DA BOOKS BRO. ALL DEM. But I'm mostly eyeing that Force one so I can possibly balance out that particular shortfall in my repertoire.
It's less 'be creative and I'll love you' and more 'be creative or I'll take my gift back, thank you very much.' If you want it to grow you have to seriously impress the angel.
((Munchkin-y idea of the day: Life magic and transformation/polymorphing, is it possible and could I use it selectively on bodyparts to turn myself into a genetic abomination of sexiness? Particularly I want to permanently harden my skin, possibly into a scaly type exterior, and possibly increase muscle mass for things like teh supa jumps. Could also go for gills/waterbreathing/other permanent natural abilities that make evolution scary and those who can force it scarier.
Related: Could those Life conduits of Lyu's be made permanent? And if so, what kind of interaction would they have with the regen ability?
There is DEFINATELY a reason you gave me the Angel of Creativity, huh? ))