I think perhaps you should stop trying to 'persuade' your boss into putting funds into a company book library. Instead, why not start a small library yourself? Purchase a book or two every once in awhile directly related to your companies past (for maintenance), current and future language/interests.
When you get a small collection going, send your co-workers a note about your small library (including your boss). Tell them your current collection and what a specific book would be best used as (i.e. learning tool, reference, etc.). Also inform them of how they can 'take out' books from your library.
I suggest setting up a sign-out/in system where a co-worker can come grab a book from your library, sign it out and bring it back later. You might want to setup some sort of return policy so co-workers don't keep the same book for months a time and require the re-signing a particular book out every day or week or so.
If space allows (and your superiors don't mind) put the library either outside of your cubical (if you're in one) or your office to trim down on an annoyance of co-workers coming and going from your personal space, if that is something that you think would bother you.
After a time, if you find that a lot of employees are taking out books and reading them, using them for projects etc., bring this data to your boss/superiors and suggest again that they get a company library going. They may now see evidence that it might be worth the money invested into it.
To even strengthen your case, you might like to get 'testimonials' from your co-workers. Something like "Without this library, I probably wouldn't have been able to use best practices to the full potential when implementing this project."