It's all about emotions. Once you have that much money sunk in a car it comes down to finding someone with lots of cash or a nice line of credit that is emotionally driven to purchase the car. Anyone with common sense will not go and buy a $19K S13 when a lot of newer cars can be had for the same amount.
I don't think there is a price limit on these types of purchases. In general the market will never support any of the older, but not classic cars, enough to make them worth the amount spent on them.
“I don’t understand bus lanes. Why do poor people have to get to places quicker than I do?” -Jeremy Clarkson