In my area, I have the Lakewood Blueclaws. Their manager in 2002 (or 01) was former player Jeff Manto. After they hired another manager, he became a part time instructor for the Pirates. He also can be hired out as an batting instructor.
You can go to
http://www.jeffmanto.com and sign up for instructions. When I mean, you, I mean the person, not the game character.
So if you can do that in real life, I think that would be an interesting addition to the game. Perhaps they could even replace the books altogether. There is obviously some suspension of disbelief that you could go from throwing AAA to a MLB caliber curveball by reading a book. But maybe just replacing those books with instructors, which feasibly could make you improve by leaps and bounds, would be a good idea.