I've recently stopped buying old books. This is partly because of silverfish. Keeping those critters out of shelves is an ongoing war. But the bigger reason is I no longer need panic that old favourites (and yet to be discovered by me old favourites) will vanish.
Girlebooks is a wonderful site making available classic books (with wonderful covers) for ereading. I've yet to buy an ereader, but I'm immensely reassured by sites such as these. When I do buy an ereader, there will be old favourites and new to dive into.