Hainzy,
I reckon you are spot on. I agree a vehicle is worth what it is and not what it has been made to look like. As long as no one is doing any thing to deceive I have no problem with it. If you are buying a matching number sandman it should be just that. Not an ex plumbers van with a different vehicles identity grafted to it.

Here's a classic example on evil bay
HG Monaro GTS V8 manual tags (saginaw) BRISBANE BUILD highly desired combo HK HT
hg tags.jpg
What will become of these? Will someone pay a lot of money for this desirable combo perhaps attached to a 161 base model monaro?

It has been suggested before and I would suggest it again that a register of dodgy ID's be started and when ever a dodgy set of tags or a completely rusted out piece of crap with matching numbers comes up for sale they are recorded and recorded and stored in a way that google can find numbers (ie not just photos but photos and text) and it may just save someone some heartache after they part with a large amount of cash for what they think is a genuine desirable vehicle.
Even my van should go on it because it has not got the original chassis. If it turns up one day with a matching chassis you can find out that once upon a time it was not matching. It will never be matching while in my possession. It is what it is and will stay what it is. A Sandman that has been in an accident and repaired with a used chassis.