Hi Lee
welcome to CAC
not ALL people are concerned about oroginality, but yes, many, many are and it does tend to increas ethe value of a classic corvette to be all or mostly original.
Many people feel that the desirablility and value onthese classic cars are enhanced by the car being as original as possible - meaning the original motor block, tranny, heads, intake, carb, alternator, starter, etc, etc, etc.
I think the idea is to be able to represent and enjoy driving the car as closely as possible to the way it was when it rolled off the factory production floor.
so many of these cars over the years have had the motors changed out, other parts swapped in, suspensions changed, etc that relatively very few of them are still original, either original parts and restored, or even more so a true original "survivor" which is a car with all or most of the original parts, still in decent condition, never restored. A true survivor car is really a piece of preserved history.
A lot of the "arguments" or debates" come in when discussing originality though and if 100 people answer you will most likely get 125 different answers.
What is original?
is it strictly the exact parts that were on the car when the car left the factory? Some people say yes. Other people are satisfied to accept originality as the correct part - meaning correct casting number and correct date codes for the part - but that part may be a replacement part from another car of the same year so the part os "correct" but it's not the true original part that the car started off life with.
Whether someone personally feels a car that is original or mostly original is worth more or not is up to them. Some people don't give a flying hoot one way or the other and some prefer a completely non-original car.
If a car is original though, right, wrong, or indifferent, the market has determined that it typically has more value and therefore typically a higher priced resell value over a non-original car.
On items like side pipes, KO wheels, etc, the same issues apply. A car that has items on it that weren't there when the car was first made will typically have a somewhat decreased value.
side pipes are a very popular item that have been added to many, many cars that didn't originally come with them because they look and sound great. Most of the time, someone who knows what to look for can determne though if the car originally was equiped with side pipes or not by a number of differences or clues on the car.
KO wheels are a bit more difficult. If you were to find and purchase a set of true original Kelsey Hayes KO wheels and they are all properly date codes within the correct date range for you car and installed them, than it would be pretty impossible to determine if they were really original to the car or if they were added on later.
To answer your final question......... Yes, it all has to do with the ultimate value of the car. An original "numbers matching" car with true original parts on it (I'm not including "restamped" parts because that is another whole issue I'm NOT going to get into) is typically worth more than a similar car that is not original.
I hope this helps a little.