Agreed. IMO, if we're taking about a sought after car like the one mentioned above, originality will affect sale price. But for a run of the mill vehicle...Have at it!
Agree with this as these are the vehicles that fall into the collector realm where originality vs modification can create a huge change in value. For the person with a '76 Scamp \6, originality and value don't go hand in hand and this is a car that may be more valuable when it is modified.
Personally, I have rarely every owned cars with a pedigree that would require an original restoration. I tend to buy outside the most desirable types so I can modify them for fun.