I've seen 6 over the years and know of one for sale locally for $6500, but it now sports a 350 Chevy, Silver paint, and is missing two of the nose grilles which are practically impossible to find.
Yeah, sadly there is a lot of merit to the things you read. These cars were hurriedly built to qualify the body lines for certification on the NASCAR circuit, next to the Monte SS Aerocoupe. Sadly, they were sloppily rushed through production and few were made. Every one I've seen has major defects around the rear window area, w/ globs of poorly applied factory filler, (which is painfully obvious under the factory paint), in the top-rear halves of the outer sail panels, (near the top of the rear glass). Yes, the tunk opening is a bit narrow, but its the same dimensions inside as every other G-body. The lack of power problem was because Pontiac was forced to use the weak knee'd Chevy LG4 305 and standard issue version of the 200R4. The 4 that I've got to climb into had an open 2:73 diff., (lacking the G80 posi). It is sad how the Grand Prix went from being one of the baddest cars on the road after John DeLorean redesigned it in 1969, stayed mean all thru the 70's, and then died a slow painful death in the 80's when they killed the LJ, the manual, and the Pontiac 301.
(Personal Opinion: had the Pontiac 301 survived longer, it would have seen a bunch of improvements. The turbo version likely would have gone the through the same improvements as the Buick Turbo 6 did, making it into one mean engine.)