Gone are the days when you could go to a local junk yard and pick up cheap replacement parts and install them yourself.
Or are they? Maybe a new generation of auto mechanics will have the electronics expertise to repair newer vehicles.
* High-end enthusiast performance vehicles. Think Porsche sports cars, Ferrari, etc.
* Popular, otherwise reliable commodity vehicles produced in massive numbers.
* Other enthusiast performance vehicles. Typical sports cars, muscle cars and sporty coupes.
* Most everything else.
* Vehicles unsuccessful in the marketplace.
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Porsches and Ferrari sports cars are in "high enough" volume amongst well to do owners, that they'll always get taken care of. That's a market that'll always pay up.
Crossovers sold to the tune of 3-5 million vehicles (in just the US!) per model generation, full size US pickup trucks, Japanese compact economy cars, etc. As long as the repair is cost effective, it will be done. Especially when a lot of modern vehicles can go past 20 years no problem if you take care of them (including garaging). It's a huge market to serve.
Then you have the bread and butter enthusiast stuff, produced in larger numbers. Mustangs. MX-5s. Toyobaru twins. Etc. These are people who have a stronger attachment to their vehicle than a normal conveyance. They're more inclined to pay more if required.
Then most other things. Simply a function of repair cost relative to market value.
Then market failures. Almost no one is going to go out of their way to save the equivalent of a Plymouth Breeze or a Daewoo Lanos.