Cockney, you need to use a bidding program... www.esnipe.com
As far as diminishing values, I believe that any quality item will not only retain value for new generations but will increase as demand will overcome supply. Maybe you do not "see" them but there is a whole new generation of collectors out there, who do not have the same interests than us, but collect nonetheless. I do not see the prices of full-size prewar cars going down unless they are boring cars, like the zillion Ford Model T that are just that and always were, a mere mode of cheap transportation. Why would anyone want to collect them in the first place? Compare that to the 1914 Peugeot Indy car that just sold 2 weeks ago far above its estimate, at $7.25 million, to a fairly young collector in Florida... truly a quality item. Great prewar racing cars sell for FORTUNES today (see the Ecurie Ecosse D-Type last year at Monterey at a cool $22 million) to YOUNG successful businessmen, These are NEW collectors.
I truly believe that slot cars (but as true collectibles, meaning new, untouched in their original boxes in kit or RTR form) will follow the same vein as long as they are not toyish or of poor design or quality. Chaparrals will always sell well, as future gens will be fascinated by their advanced technology for their time, 20, 30, 40 years from now. And these people will want anything that raced with the Chaparrals.
Thing is, these new collectors will look for what is best out there. Such new collectors will likely bring prices up and up, while lesser models will likely lose much of their current and often excessive values.
But I see that prices of currently over-valued so-so models will tank.