First I'm not wanting to hijack the thread Glen. I just wanted to give you my opinion from the industry.
I think this post brings up a good point. To restore or not to restore I guess would be the question? The restoration industry has boomed then slowed over the years. Now most of the shops left are the ones that had solid followings. There are still some cropping up here and there.
There has been a growing trend to original vehicles more now with the cost of restoration. You have to go big or go home when it comes to quality of a restoration for serious collectors. Many cars aren't worth the cost yet.
It should be the responsibility of the facility to properly evaluate a vehicle if it is a canidate for preservation or restoration. Some places may be too eager to restore for that bigger paycheck. A preservation is still a big job but not as big as a restoration. Seriously discussing the fallback with the owner if they are set on restoring a preservation canidate is important.
Some things to look into would be:
Past repairs and quality of them if any.
Does the vehicle retain much of its originality?
Can these areas be preserved or brought back to an acceptable condition and remain that way?
Is the vehicle structurally and mechanically sound?
Is the vehicle safe to drive?
History: Rarity, Desirability, Availibility of OEM (not reproduction) parts
The Ferrari mentioned I would assume was prior in a functional state cosmetically and mechanically. This would be one reason it's value would turn. Many enthusiats of Ferrari want to be able to dirve them. It is fairly accepted to rebuild the mechanicals but preserve the cosmetics without hurting value. Many mechanical items have been replaced or repaired through regular service when they were just cars to people.
The other end of the spectrum is restoration for resale (auctions, etc). With the muscle car boom there are multiple reproduction parts availible. Many shops would simply go through a catalog and order everything new. It was cheaper than repairing the old. This is a two fold problem. First many original parts were repairable but time and money beccame a bigger priority. Second in order to not cross the official endorsement of a manufacturer they had to be different some how. IE; metal thickness, stamping, moulding. Shops would simply replace and resell original pieces to balance out a larger profit at resell. (Just browse through E-bay) Now you end up with a vehicle that retains much less of its original parts.
Granted companies like Dynacorn and GM endorsing places that have acquired the original tooling rights have helped in quality. The question. Is a 69 rust heap Comaro or 67 Mustang for basic parts to put in one of the complete bodys plus extra new parts after the vin is switched the same car. No IMO. This is why there is a cloning problem.
A new "reproduction" VIN should be issued and old one filed as "parts" in the case of a reproduction body. This would protect uknowing future buyers.
My philosophy is to preserve as much as posible. If restoring documentaion is key. Use as many NOS or OEM parts as availible. If replacing trim, etc. due to cost, keep the originals with the vehicle. There may be money or new owner to fix them later. This will also preserve some value.
The biggest thing on value is simple. It takes at least two people to desire the vehicle. If the owner is the only one who thinks its worth something it doesn't sell.
I wasn't trying to rant but just give some insight of what I've seen on how restoration can affect value. Certain vehicles done right can also go through the roof in value.