I think this is a nice idea, but despite the apparent number of enthusiasts on this forum, across all retro interests, I think the actual uptake would be pretty low.
However, if it could be tagged onto another show, something like Bespoked in Bristol, or a transport museum open day / weekend, then I think there would be not only a draw for the non-retro aware, but also additional exhibits of interest for the retro crowd.
The choice of venue would be a tough one, York rail museum? The National Motorcycle Museum in Brum? Brookland? Beaulieu? Haynes museum in Yeovil? The choice is almost endless.
P.s. I like the idea of a Jo Burt / Mint Sauce exhibit.
Brooklands have a historic and classic display at their September Cycling weekend, organised by the VCC. I went last year but it wasn't that good in my opinion - but I'm probably over-influenced by our own Yorkshire Classic Show.
Today is the yesterday of tomorrow.