I think a fundamental difference is people hoard cars a lot more since the 80's. People had already seen older cars go through a redneck yard junk phase followed by a shortage and people stashed g bodies and prematurely thought they had something valuable on their hands. Which is why I see people obsessively garaging ragged out cars and base models and sellers asking insane prices. IMO it'll take way longer if ever for gbodies to reach rarity of past generations of cars.
The problem I tend to see is people afraid to enjoy their cars whether its fear of rain or theft.
I agree with you that some thought when the performance resurgence was going on in the mid 80's that in 30 years it would be a repeat of the high prices the 60's muscle cars were getting. Nostalgia and what many saw as the end of an era had many craving 60's muscle.
In my opinion the only way that would have happened to the 80's cars is if some kind of gas crisis or crazy insurance rates would have had cars basically being like Ford Escorts in the 90's. Instead cars and performance continued to develope to the point you can now buy a high horsepower car with ac, adjustable suspension, good mpg and no foreseeable end to performance of future car models.
What keeps me interested in my SS still today is what I mentioned before: nostalgia. Plus the fact that after 30 plus years my car is not something you see on the road everyday. It is unique because of time but does that make it valuable? For me I could not put a price on my car but in the marketplace the only G bodies I see making insane money are the late 80's GN and GNX.
Just like the old saying of how much is my car worth depends on what someone will pay for it. Recently a very low mileage SS was on Ebay and the highest bid was around $10,000 where I believe the owner wanted $24,000 in the reserved price. Is that a good price? Is it just plain nuts? I do not know?