According to the Pinpedia.com data base of sales. If you bought a WH2O 10 years ago you could have gotten it for about $900.
You could sell it now for $2500 unrestored.
10 years from now if you have one in good shape...who knows. It's not like they are making any more. As a matter of fact they didn't make enough for the home collectors who are flocking to get one. It's about supply and demand. How many WH2o's will be working in 10 years?
I predict the top 10 machines, including WH2O, will all be worth between 7k to 10k in 10 years. Those are the ones everybody wants.