It's not the age of the fabric that determines the price... its that old supply and demand thing. It's out of print, so what's out there is out there and there won't be anymore. Some writes an article about it, or shows a pattern with something made from it and suddenly everyone wants to have it... and again, just because it is worth that much today doesn't mean it will be worth more or even as much in a year or so... by then, the trendsetters will have moved onto something else. I saw it first hand with the Rose and Hubble flower fairy and William Morris prints a few years ago. Today they sell sell for a lot, but not as much as they did a few years back when EVERYONE wanted them!
If I owned some of this fabric and wasn't absolutely in love with it... I would jump on the bandwagon and sell it now on eBay and use the money for something else that you want now!! The people selling it on eBay now probably bought it by the bolt at a wholesaler after it was discontinued. So, they will just keep selling and relisting until its gone.