I'm inclined to agree. This is the answer that Occam's Razor would give us. Especially given the fact that this aircraft was designed so long ago.
It would be one thing if we were reading leaked documentation about an experimental aircraft designed 10 years ago. But we're not. We're reading declassified info about an aircraft designed some 50-60 years ago. If it actually worked, a half-century would be a pretty reasonable timeframe from experiment to slightly more mainstream application. If not commercial application, than certainly military or scientific application. And its existence would have turned up by now. Alternatively, it would be so effective and groundbreaking that it would remain classified to this day, and nobody would have declassified any of this documentation.
EDIT: From the (extensively documented) Wikipedia article on the very similar Avrocar:
"In flight testing, the Avrocar proved to have unresolved thrust and stability problems that limited it to a degraded, low-performance flight envelope; subsequently, the project was cancelled in September 1961."
Additionally, if the "saucer" had any reality to it, the F-35[1] program would not be the mess that it is. It's performance is half the "saucer's" purported performance[2]: short takeoff / vertical landing (STOVL), half the maximum speed, slightly more range (which it is struggling to achieve), approximately half the service ceiling (and the range and service ceiling are probably for the conventional "A" model, not the STOVL "B" model).
It would be one thing if we were reading leaked documentation about an experimental aircraft designed 10 years ago. But we're not. We're reading declassified info about an aircraft designed some 50-60 years ago. If it actually worked, a half-century would be a pretty reasonable timeframe from experiment to slightly more mainstream application. If not commercial application, than certainly military or scientific application. And its existence would have turned up by now. Alternatively, it would be so effective and groundbreaking that it would remain classified to this day, and nobody would have declassified any of this documentation.
EDIT: From the (extensively documented) Wikipedia article on the very similar Avrocar:
"In flight testing, the Avrocar proved to have unresolved thrust and stability problems that limited it to a degraded, low-performance flight envelope; subsequently, the project was cancelled in September 1961."