Asking from ignorance...what do restorers actually do to the cars?
Is it a "ship of Theseus" situation where all (or at least a lot) of the parts are replaced and the visible body is patched, sanded, and refinished? Maybe a new body panel here and there. Seems like as the restoration becomes more effective there is less of the old car left.
Well there’s many types of “restorations”.
Also depends what was there when you started. Ideally it’s all there, and just needs work to bring it back.
As some older cars get more expensive, exactly what you do needs more thought if it’s to be sold vs drive.
A true restoration seeks to basically make it like it was when running during the time period, or even as found, but… better. It’s clean and maybe runs. It can get complicated and require expert knowledge of the car and market. “Do no harm” is probably only recently coming in for many cars. If you found a rare Bugatti in a barn say, you don’t want yo go out and make it all pristine. But if it’s trashed, that’s different.
It’s actually more desirable to keep original paint. But people only do that if it’s really worth a lot, and it does get complicated. There are many quality “driver” restorations that make it better than it ever was. Also poor ones. The word “restoration” really has little absolute meaning by itself.
These days you can totally upgrade many cars’ brakes, suspension, steering, engine, and still keep it looking mostly stock. Those ads that show up for 1960’s Broncos for $125k+, are basically an old body repainted better than the factory with new drivetrain, steering, brakes, that are all modern.
I still have regrets over going into the auto parts store around 1981 with a friend, and looking at a Ferrari parked out front. A 1960’s 275GTB. Beautiful car, not your “common Ferrari” one saw at that time. It didn’t look good, but from outside, it was all there. Paint totally trashed and even gone, but body not really dented, inside trashed with cigarette butts everywhere, but not missing major pieces. In the store, we found out it was owned by a mailman. He wanted $14k for it. It was just out of the question.
These days the car “restored” is likely north of $1 million. I see one sold last year for $3 mill. Oh well.