I'm pretty sure you have never driven any 356 Porsche spiritedly for you to think they had much in common with fiberglass replica. To call this a "gussied up bathtub VW" would be like calling the Bullitt 390 Mustang a "gussied up Falcon". By 1958, a T-2 Porsche probably shared 50-100 parts with VW's. Of perhaps 5000 parts.
All of this only serves to undermine the classic-car industry. More and more stories surface constantly about high-priced, misrepresented cars. It will get to the point that people will just give up on all of this madness.
I've always been involved with Corvettes. One of the most popular and valuable years for them is 1967. There were 22,940 total cars made for that model year. But I would swear I have seen 22,940 1967 Corvettes with the optional 427/435 HP engine at Barrett-Jackson and Mecum.
I've never had it happen to me but I cannot even imagine the sinking feeling a buyer must get after he spends big money for a rare and desirable car only to find out later on that it's NOT what it was claimed to be.
People like that probably never recover from it and probably never jump in the water again. You know there is a Muscle Car explosion going on right now with new cars. So, it would be easy for a lot of those who got burned to switch and never look back.
When Porsche built these cars it was a real "hobby shop". They had precious few records and even fewer kept. Now about the most one can get is a "Kardex" from Porsche, possibly some records from Reutter (the body/ chassis builder). The very best information/ provenance about these cars is held by a few restoration people. Mostly US people, perhaps a couple in Mexico, Argentina and Europe. The 4 cam cars were essentially all race cars and they have been used up/ crashed/ discarded for 50 years now.
Minor correction: Carrera GT's do not have aluminum bodies. they have aluminum hoods, doors, and engine lids.
America Roadsters and Gmund coupes and Spyders have aluminum bodies. Genuine 356A GTs have a few subtle features that might get past a cursory inspection.
Does being the infamous "Seinfeld Fake" now give this particular car a value bump despite it's shady history?
We haven't been told what actually makes it suspicious. Might be something future auctions just gloss over "there are some concerns around the authenticity of this car, but it is so beautiful one just has to forgive it and make a bid anyways".
I say a rich person with no intentions to drive it sees this as the perfect living room discussion piece, next to their live edge oak Kramer head.