To me, it has everything to do with whether the wear is normal and honest, or whether the firearm is pitted all over, rusted, busted, and has been abused by somebody who had no business owning a fine S&W. If the former, I will generally do nothing except give the gun good care and catch up on its maintenance. If the latter, I will not hesitate to restore it as best I can. In my opinion, the only time it is wrong to restore a gun in very poor condition is when the story of how it got that way is a part of its historical provenance...especially within a family.
I firmly believe it is silly to take the rigid, purist position that it is always wrong to fix a broken or abused gun, or anything else, no matter what. One size never fits all. I have yet to hear one of these don't-touch-it people persuasively explain why nothing restorative should ever be done, beyond "just because..." or "it ruins the collector value." Who cares about that viewpoint? It's an irrelevant minority one. If they want to pass, fine. 20 reasonable people will be lined up to buy it at a reasonable price; or these days, even at an unreasonable price.
But I have to say that after a very old gun passes a certain age, maybe it should be left alone, to rest in peace. How old? Don't know.
And I don't support those who grind up fine old guns in the restoration process, or those who misrepresent them as original, when trying to sell them. That's fraud. And there's too much of it going on at any gun show, even the more reputable ones...especially on the part of guys acting innocent, who did it, but plead ignorance about the gun's history; "I dunno, just traded some guy for it. Looks pretty original to me." Sound familiar?
Reputable collectors should get together in a group effort to write a book about all the ways to be ripped off at a gun show. I've often thought about that. It would be a thick one, and would have most show promoters in a boiling rage, since so many are willful enablers and knowingly tolerate the abusers who rent tables, show after show, year after year. That is what gun shows have become, in a competitive and often desperation driven market.
Seriously, just when I think I've seen most of the tricks after a half century of prowling shows, I find I haven't. I would estimate that 30% to 50% of all the guns I buy at shows, even now, turn out to have intentionally concealed defects which I was not able to detect until detail stripping the gun at home. Gun shows have become dumping grounds for cosmetized trash. Misrepresented refinishing is a small part of it. Shows and table holders have changed so much in my lifetime. So what do I do? I fix the guns, write it off as part of my continuing education, keep attending shows, and keep trying to detect the rips before I become the ripee.
And if even thinking about buying over the Internet, hang onto your posterior with both hands. Rolling dice at Vegas is lower risk entertainment.