80's GM's feel the same as 70's GM's to me. No one complains about the shitty interior on a 'classic'...I mean, you might love the look, but the materials, fitment, ect are all going to be generally worse than most any modern car.
Cardboard door panels with some carpet remnants and some poor quality vinyl. Maybe a metal strip or two. Awful plastic consoles and dash pieces. Cardboard glove boxes. Ect.
80's GM's, as least F-bodies and most full frame cars, are pretty solid. My firebird still felt like a big metal tank to me. Much the same as my previous 70's A-body, just with more grip.
The late 80's FWD on into a lot of the 90's is what is really awful GM. Starting to build things 'new school' but it took them a while to get remotely decent at it. Early 90's GM FWD....uggghhh...arguably set the bar for cheap, squeaky shittiness. But it was a competitive (in shittiness) market.
I dunno why the 'vette prices tank so much. I guess the relative 'exotic' nature next to other front engine, RWD candidates of the period probably shrinks the market...80's G and F bodies can be used like 60-70's muscle cars- it's just a simple, fairly sturdy rolling platform for whatever engine you wanna stick in it.