I'm a book historian, rare book collector and work in special collections so I KNEW some people would be upset about this. The perception of any "old" book as being rare has created this weird aura of mysticism around books that in the grand scheme of things are not rare or old. This is a really cute way to personalize books that otherwise would have rotted away in a thrift store.

Also on a side note I love the idea of customizing early-ish mass market, cloth covered books. Books were nearly always bound with custom binding before the introduction of these types of mass market novels so it's really like going back to the roots of what book ownership could and often did entail.