Most of my bird hunting gets done with an 1880s German Hammergun that was sound but totally nonfunctioning when I received it. All it needed was the accumulated gunk cleaned out of the lock mechanisms and triggers, a new wedge made and a hammer tightened up on the post. It's certainly of higher value now than if it had been left alone.
Right now I'm waiting on delivery of an Original Percussion Westley Richards SxS that looks to have had rough treatment in the past but still has lots of meat left on the barrels. It's super plain ( I think for a while they offered their equivalent of a hardware store shotgun), no engraving, AFAIK was not owned by anyone of note and has no particular collectablility or historical significance other than being the most basic, cheapest gun offered by an otherwise high end maker. I intend to make it back into a bird killer, just as it was intended to be. Being able to be used again certainly must be of of greater value than an old brown gun that happens to have a well known name on the lock plate.
I can certainly see the value in maintaining the originality of a rare, decorated example of a piece by a known or unknown maker. Its very existence contributes to the pool of knowledge in the subject both now and in the future. A "restoration" could destroy some yet undiscovered piece of information or simply diminish the value of that part of history. I also can't imagine "cleaning up" Andrew Jacksons Pistol, a rifle documented to have been at the Alamo, a Boutet flintlock double gun or Kaiser Wilhems boyhood rifle in any but the most extreme circumstances. But I don't think all guns automatically warrant such reverence just by virtue of being old. If there is nothing to be gained from leaving it alone but it could be brought back to life as an interesting shooter with lots of character then that can't be a worse option.
that's my feeling anyway, or at least my hamfisted attempt at putting my feelings into words.
(Edit)PS: I'm obviously not talking about a crappy restoration, bad work is bad work. Or work done with no attempt at all to be appropriate for the original time period. I also have a really nice Belgian shotgun that had been "restored" before I got it. It should be a MAGNIFICIENT gun, save for the very well done but totally inappropriate modern checkering profile left by the checkering being freshened. The birds don't seem to care though.
