I think prices are relatively stable, except for a handful of icon and heavily in demand, genuinely scarce books that rarely turn up in any kind of decent shape. Even Strange Tales 1, a book I considered to be very tough to find even in VGF has turned up on ebay in the FN range three times in the last couple of months (admittedly after a year long absence). Prices weren't too far from guide, although guide is high on that book......
On the other hand there's the Gaines File Copies - the horror / crime titles (especially books such as Crime 22, Shock 6, Crypt 17, Vault 12 etc.) go for crazy amounts if the book is 9.2 and above - certainly more than the Sc-fi or War books. That market has never cooled off.