Library Swallows House! Story At Ten

Upon moving to my current home in 2010, I made two decisions related to my book collection:

1.) After a lifetime denying myself the pleasure, this home would include a library, i.e. an entire room dedicated to my collection, complete with floor to ceiling built-in bookcases. My lifelong friends would now get the space they'd always deserved instead of lying in random piles in every room.

2.) To ensure I did not become the subject of a future reality TV show about book hoarders, every new book purchased would be coupled with an old one donated to a library, coffee shop, etc. And that brings me to my current dilemma.

Up until now, it's been relatively easy to decide which of my friends would give up their space as a purchased book was added to the shelves. The earliest donations were books my wife had read that I was reasonably sure I would not. Before anyone calls book foul, let me clarify: She is not as attached as I to books she's finished. The second phase of donations included stuff I'd enjoyed at the time but  probably not much worthy of a re-read. 

I'm now in phase three - decisions about what goes next are becoming more difficult. Either ... a.) I've read it (or in several cases, re-read it) and my notes and annotations are part of my story or ... b.) I haven't read it but I'm pretty sure I will or ... c.) something unexplainable won't allow me to let go ... yet. Any book hoarders care to offer some coaching? Good thing the public library and my thriftiness helps me keep a lid on purchases, huh?