After getting deep into my frame off I have to agree with the editorial in the new HPP mag.
Only the VIN tag holds value. Other than a few rare parts every other piece can and probably will be replaced on a resto.
So what do you really have? It's not a restored original unless you used the original parts. That is near impossible on I'd say 95% of the restorable 40 year old cars.

Door panels will probably have water damage on the back side and are usally dry rotted to the point of not being able to re-use the cover.
Seats are the same way. Headliner? Forget re-using that.
Re-chrome bumpers vs repo? Cost is significant, most use repo now.
I just used those as an example. The list could go on.

Unless I'm going for a concourse rare car I'd rather start with a clean straight lesser car and build what I want.
You'll rarely make your investment back on a rare resto, the price is to high for the car unless it's a barn find, which is about like winning the lottery these days. Everyone thinks their car is a gold mine, yes restored it probably is valuable, but getting it there will cost you more than the selling price.
The only people making real money are the ones selling the ones needing restoring. Unless you're Foose or some other high end shop.

Awhile back a guy on Hotrodders said he went to look at a 1970 GTX he heard about, said it was at best a $5000 car, needed everything replaced but most everything was there.
The owner said he'd take 25, he wrote him a check for $2500, the guy said no, $25,000
Said he'd seen one on Barrett Jackson sell for $50,000 so his was worth at least half that.
The buyer said it would take at least $25-30 grand to restore it so he told the guy good luck and walked away.
Last I heard a year later the car is still sitting there, rotting away.

Barrett Jackson has been the best and worse thing to happen to cars in the last decade.