You're reading more into those auctions than you should. The folks buying those cars aren't savvy collectors, they are dealers and speculators and a smattering of so-insanely-rich guys that they "just don't care" what the price tag is, but amusingly, are TOTALLY out of their league when it comes to speculating and predicting what will hold value long-term... Tons of cash, not much car sense.
Those sales are anomolies, and they do not cement the Unique Performance cars as future goldmines... They just represent the 1st chapter in a playing-out story where at some point down the line, estate auction, collection liquidation, a car that was foolishly bought at auction for over $500K sells 20 years later for $60K, in 20-year-later dollars...
The other folks who are buying the cars directly through Unique are not collectors, they are rap stars, rock stars, dot.com guys, folks who don't know squat about what makes a car a future classic, but think that by virtue of it being signed by Shelby, they've got something..
Never be fooled by "hot", when it comes to pop culture flashes like Eleanor. Let's be honest here, Ford stopped producing 1st-generation Mustangs 35 years ago. The new "Shelby-Authorized" Shelbys are just old shells restored into hotrods, and Shelby is only in it for the money. There's little parallel to the original Shelbys, that will always hold supreme reign over the here-today-laughed-about-tomorrow Eleanors...The original cars will always have desireability, provenance and classic status, the Unique Motorsports cars will just be what they are... Resto-mods authorized by Shelby...
There's a HUGE difference between what's "hot", and what goes on to be classic and timeless.. The Monkees were "hot", and even topped the charts for awhile, but no matter how closely they patterned themselves, they never were the Beatles, were they? But back then, the teenage girls didn't seem to care...
I view somebody tossing $500K++ toward a Unique Performance convertible very much like a teenage girl back in 1969 in the front row of a Monkees concert tossing her bra at Davie Jones... Lost in the moment of a humorous obsession...