People can argue about it as long as they like. The reality is always that the value of a used car is what someone will pay for it. Everything both before and after the money changes hands is best guess.
I would assume that those arguing that the car isn't worth it wouldn't pay that much for it.
The value of a used car also gets more and more variable as time goes on, and in some cases is also VERY regional based on condition. A beat up or rusted car isn't worth much anywhere. A car in pristine condition is probably worth more in places where conditions are conducive to rust and corrosion. I live somewhere that has salted roads, so even in midsummer, the rain can be depositing salt on the car, and there's always dirt and sand, so old cars with nice paint and no rust will go for a premium, for people who have a particular interest in them. Go out to the coast, and those cars start getting much cheaper. Sure the ocean air is somewhat salty, but the moderation in temperature means that they don't have large fleets of trucks pouring salt (Or potassium chloride) and gravel on the roads 6-8 months out of the year, so the cars get fewer paint chips, and rust start points. The same car in much better condition becomes much more readily available, and is therefore cheaper, until the difference in price pays for transportation and/or out of area inspection charges. (My last Supra was imported from the coast, and was probably half the price of what I could have located one locally in the same condition.)
So there's that, too.
Some people don't really care about "one owner" and so it doesn't increase the value of the car to them. If that's a part of what you're setting the price based on, then you're restricting who you're marketing the car to. (It turns out that |I'm the second registered owner of my 2012 Focus, but I think from recent events, it might well be that there's a reason that the guy traded it in.)
Any used car is going to be worth more to one person than another. I'd might have paid a little more for a car that would match one of the sets of nice wheels that I have in the garage, or fit the aftermarket roof rack and carrier, or if I had performance or interior parts for it already, or of course had some sort of emotional attachment to the make/model. If you can find THAT buyer, then you can get a very good asking price. I've had cars that I assumed that I'd never sell, because "nobody would ever offer me enough." -- then someone did.
The monetary value of a thing is always the point where the owner will take the money, and the buyer will pay it.
2012 Focus Titanium Hatchback
121,000 km, all stock
1990 Toyota Supra turbo
I think the cams are still stock...