In the book The Count of Monte Cristo. Abbe Farria reveals that he rereads 150 books over and over again. I think having a large library is awesome if you can afford it, and have the space for it, but I also think that re-reading the same books over and over is also helpful.

He says:

The idea of 150 books for a lifetime of reading: “I discovered that one hundred and fifty books, carefully chosen, give you, if not a complete summary of human knowledge, at least everything that it is useful for a man to know.

I think my personal library would be more to the tune of 75% read, 25% on deck, or "maybe someday."