The reason pro-street car values have gone down is that people figured out that they are no fun to drive more than a few miles.
There will always be a demand for well done classic cars that contain modern road manners and comforts. As long as pro-touring does not make the same mistakes as pro-street it should continue for a long time (evolving further along the way)
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"A ship in port is safe, but that's not what ships are built for."
See Bad Penny run the cones:
https://www.youtube.com/watch?v=8GUPPIX-92U
1971 Chevelle Wagon - Roadster Shop Chassis ProCharged Shafiroff LS and lots of yada yada
1968 Camaro - Project Track Rat - 440 RHS LS