Well, Peter Walsh in his book It's All Too Much (yes, I've sent for it - don't laugh!) says you keep all those books so that when you reread them you will remember the great times you had at university, or because you might need them someday, or you have always had them so you can't part with them, or someone gave them to you so you are obliged to keep them forever........
I simply love them! They represent many hours of enjoyment, which is lovely, but do they give me joy now? Just being there? Maybe not.
Someone else once said your books should represent who you are now, not who you were 10 or 20 or more years ago. Good point. I've absorbed much of what I needed from my books I think. This is something I'll consider as I go through them deciding whether or not to keep them.
This weather is perfect for the task. Feed the birds, then a good fire and a mug of coffee and I shall set to, but first....