i ended up completing the game with no upgrades other than the amount of books i could hold and i had a fantastic time! i'm sure my experience is out of the ordinary but it was a fun, relaxing, repetitive project that took me about a half a day, spread out over multiple sessions.
i agree with a comment below that most of the upgrades feel like "would you like to play the game less", but i don't have any ideas for how that could be improved
ido also agree that having similar-looking books be related subjest or something instead of completely random would be nice
i enjoyed the game, but seeing as i played in a way likely not intended i dont know how valuable my opinion is ^^;