This is a good question, especially since these bikes are getting some age on them. Even though we're still finding low mileage bikes, we really don't know the history behind them. The seller want to get as much as he can, and the buyer wants the best deal he can, but what is true value.
I look at it this way. What did it cost new, what is the average price now, what would it cost to build one exactly like the one I'm looking at, and what am I going to do with it when I get it?
There really no reason these bikes that are selling for $10,000, shouldn't sell for $18,000, considering, they were $34,000 new, and many thousands of people thought they were worth it back then.
Basically what it boils down to, you look at a bike you like, you'll pay what ever your love level is for what your looking at, and what your pocket is comfortable paying.