If I remember correctly, Lois McMaster Bujold never completed college. A couple of years ago, she decided to take a college course on medieval Spanish history "just for kicks" and her study of the life of Isabella of Spain gave her the plot for The Curse of Chalion. Which as you probably know, did quite well for her, being a finalist for the Hugo and winning the Mythopoeic.

So even just a smidgen of book learning can be grist for a good writer's mill.