In today's market, buyers, as well as builders of these "upper
level" cars are very knowledgeable and want their cars to be 100% correct
in every possible way. They want vehicles that are not only numbers matching,
in respect to motor, trans, and rear, but they want every body panel, piece
of glass, engine component, etc to be correct. Cars at this level of correctness
are few and far between. Just think about how many cars were in front-end
accidents and had the sheet metal replaced. I am sure you get the picture.
These pristine examples are being sold for amounts far exceeding the prices of vehicles that are restored to "perfect condition", but with non-date coded correct parts. For instance, many 1970 GS cars have had the radiator core supports replaced with NOS units. All these replacement parts are of the 71-72 type, they can be used on 70 cars, but they are incorrect.
This means if you are building a totally correct car you need a radiator support that is not only correct for year, but also date coded correct. I am sure you can see the problems/added expenses that go along with something like this. That's why the unmolested high performance cars sell for such premium amounts. The less correct original parts you need to buy the better off you are.
Where people get into problems with restorations is when they spend LARGE amounts of money purchasing NOS parts that are not date coded correctly for their cars. If a knowledgeable person checks one of these cars over for a perspective buyer, the car that looks beautiful and correct turns into what I call a Scatter Skeleton. It ends up looking like it has a part from this car, a part from that one, etc.
Another place where people get into trouble is with restoring the wrong cars. If your car has an incorrect drivetrain, or is a commonly found example, it doesnt matter if it is restored to Concours show condition. Yes, it will win trophies, but when you decide to sell it you will not get a good return on your investment. It would be wiser to restore these cars to a lesser level, where they can be driven and enjoyed.
The practice of having someone check over a car before purchasing it is becoming more and more common as prices for these pristine cars climb. I get calls about this all the time, and at the GS Nationals I usually examine at least one car this way. There are people that fly all over the country checking out cars for buyers. They charge hefty fees for this, but this expense is nothing compared to being stuck with an incorrect car. It takes years to accumulate the knowledge required to do this, and these experts should be and are compensated for their time.
Currently it is very hard to restore a 60s or 70s Muscle car to this level and get your money back when you sell it. Only a few ultra rare varieties can get away with this, however this may not hold true in the future. More and more upper level buyers are interested in buying correctly restored Muscle cars, and are willing to pay good money for them. The supply of these cars has always been extremely limited and if demand continues to increase the cars that are 100% correct will command very high prices.
If you are contemplating one of these restorations, do your homework. Make sure you pick the right model, and that the vehicle is original enough to not make the restoration a monumental task. Restorations are tough enough at any level. You get the idea.