I think that one of my reasons for general decluttering is to make room for books! I am sure we have more than 1000 "keepers" now.
If I know there is no chance I will ever want to reread a particular book, I will put it back into circulation. I sometimes sell them to a used-bookstore, but mainly donate to the library for booksale fundraisers.
My husband's aunt has a shelf near her back door for book giveaways - if a visitor wants a book that is there, it's theirs. If I had more visitors I would do that too.
I don't actually buy books very often. I visit several libraries on a regular basis, and we usually have 20-30 library books on hand: the latest bestsellers, a few piles on some topics I want to research, plus some items DD picks out.
We are building a house soon, and I want to have lots of built-in shelves for books throughout the house. I think everything will look less cluttered with uniform shelving, so we don't have stacks of books on every imaginable surface.