C) and B) are the greatest offenders for me, I think. I have a number of very old books that I have not even read yet, but have a sort of emotional attachment to their age and relative rarity, thinking of them as documents of the past... I have a writers' Who's Who from, I think, 1949 I chanced upon in a Prague bookshop for the ridiculous price of 5 CZK; it serves as pretty much nothing else but a weight and a curious proof that in 1949 Lewis was in a writers' Who's Who and Tolkien wasn't.
And then there's all those childhood books that I haven't touched in years.