So now we're into the old argument - "glass is class" versus "steel is real"
However - as swvalcon noted - the vast majority of folks who are interested in hot rods now just cannot relate to something from that era (or even earlier - T's & A's are just not the objects of lust they once were.
Even the shoeboxes are not really in as much demand as they once were either - but 60's Stangs and Camaros - wow! Around here, '57 Chev's are half the price they were a few years ago, while a '67 Camaro seems to have doubled. In my frequent travels through Wa, Or, BC, Alta, Idaho etc I see 30's and 40's cars sitting for sale. A year later they are still sitting there. I see a '55 Dodge sitting for sale for 3 years and still there. When I see a rusty '67 'Stang fastback sitting for sale on my way TO somewhere, it is usually gone by the time I am on my way back. Maybe the owners of the ones for sale for a long time have weird ideas about price, or maybe there is just not enough interest. I suspect that if a '29 A, a '38 Deluxe, a 57 Fairlane and a 67 Mustang were all for sale at the same price, (in roughly the same condition) the pony would sell first.
If there is reduced interest in 30's cars, there will be reduced sales of them whether they are steel or glass.
Prediction: the body molds will somehow make their way to a certain un-named other country (that is now making and selling fiberglass RVs into the North American market) and prices will fall.