cant compare aluminum treks to the steel ones.
Also, that is jut a true temper frame, not a reynolds 531. He's asking the highest side of reynolds 531 frame price for that bike, probably because he looked up "520" online. The frame material and small details of each model year, and frame sizes are why you see some bikes commanding a premium on ebay.

I find that ebay does a good job of setting the market or many bikes as wishy washy and those with lack of knowledge don't bid effectively.

It does have cantis and eyelets so that's good and will make a nice tourer, but its not on par with the older offerings. I'd value it at $375 but of course market location is important as well. If it were reynolds 531 it should warrant $500. For that pricing it had better have new cables and housings, new tires and grease.

Its a bike worth having if its your perfect size and you really want a tourer. Its not a bike worth that type of premium, especially when the owner only hauled it off the garage wall and dusted it off. You may not be able to convince him of that though so you may still wait some time.