I wouldn't class it as upkeep, once their arranged on a shelf they go untouched. They are beautiful books and I love having huge chunks to read in one book.
I clean all my crap every few months anyway and the way I see it is they give me enjoyment so I look after them. I've had the same guitar for eleven years. It's done hundreds of gigs, thousands of practices, tours, recording and it only has about four marks on it and they all happened during gigs, the only time I think it's worth risking any damage. It doesn't hurt to take a bit of pride and care in things even if they aren't items that are supposed to be exposed to wear and tear.