On my 2nd account, I put out 10 libraries plus old Thomas. One is level 5, one is level 2 and the rest are level 1. I'd rather put the resources towards multiple libraries than upgrade existing ones. With 10 libraries out, I'd occasionally get 0 books and rarely get 3-4 books. Typically I'd get 1, maybe 2 books per collection. It takes a lot of books to upgrade to level 5, (75 for the last level) as I'm sure you know.