If nobody buys $35,000 cars, where does the supply of reliable 10-year-old $5000 cars come from?
If the aggregate demand goes down for all the cars, prices should also go down across the spectrum (to varying degrees, but still)
But the question remains, if everyone who bought new cars kept them for 20 years and drove them a lot, what would the used car market look like?
I've seen people commenting that the money you save on buying new just goes on repairs instead: I don't agree. There's a fashion and entertainment value to driving something that works just as well as a new car but is newer, so the market gets pushed down.