Spent an hour this morning looking for second hand chess books at the 2008 Lifeline Bookfair. Unlike previous years it was slim pickings. I found 2 books I didn't have amongst the 6 or so books in total. One of the books I did get was a signed copy of 'Nigel Shorts Chess Skills', although it wasn't signed by Nigel, but by local players Ian Hosking and Ian Rout. Maybe that makes it more valuable, but somehow I doubt it.
But one thing I did notice, and indeed always notice at second hand bookfairs/shops, is that there always seems to be plenty of books on Bridge. At most place I frequent the ration is usually 3 or 4 to 1 (ie for every chess book there would be 3 or 4 bridge books). Now the cause of this isn't that there are more bridge books than chess books in circulation, as far more books on chess are published than bridge. However it could be that there are more bridge players to buy books in Australia than chess players, and this may be true, as bridge tournaments have a far greater entry then chess tournaments. But that only explains the purchase of books, not their disposal.
My (morbid) theory on the disposal of bridge books is that these books are entering the market via deceased estates. And as bridge players are on average older than chess players, this happens more frequently for bridge players than chess players. Of course I could be wrong, and by applying Ockhams Razor (the simplest explanation is often the best), it could be that bridge players just care about books less then chess players do.