[quote=Risewild]
Change the money reward for each book from 100 to 10 caps (like scrap metal in Megaton) then instead getting 35k one gets 3500, no more exploiting around.
[/quote]
I think 10 caps for a pre-war book is kinda chump-change. Sure, to the average wasteland illiterate, pre-war books might only be akin to unappreciated picture books (like ancient Egyptian scrolls discovered in the 19th/20th century by the Arabs), but to the right people (BoS, for example, like the scrolls to the English et al Egyptologists) those things are priceless.
As a Vault-Dweller, as opposed to the Arab, we'd know this.
However, the idea of diminishing returns is a nice way to counteract that, internally justifying it by the fact that, either, hey, the BoS only has so many caps on hand, or something along the lines of, yeah, these books are really useful, but at this rate, we'll really have a lot on our hands, and so on.
In FO3, I really thought that 100 caps was a rip-off for a piece of pre-war history and knowledge, and ended up always keeping the books myself.