I am currently sitting in my library - we converted the garages when we moved in, and one was a den for the boys, and is now dh's office, and the other was my library - books on three walls, floor to ceiling. We also have at least five other bookcases scattered around the house, and they are all full.
We are planning to put new shelving in the library, when the money from mum's estate comes through - we've found a really good, flexible design that is shallower than the IKEA shelving we're using now, so will make the room a bit more roomy. Doing this will necessitate packing up all the books in here, and I am going to take that opportunity to weed out the ones I'm not going to re-read, and make a bit more space.
As you say, @MarieDeGournay, if I find I do want to re-read a book I've got rid of, I can go to the library or get it second hand or on kindle.
I'm on a thread at the moment about books posters thought no-one else had read - it is a cornucopia of memories on there, and I have added several books to my re-reading list.