It depends on whether you consider a gun an 'investment', a tool, or an object of art. Also depends on the gun.. American collectors are obsessed with originality, but many other places (i.e: UK) refinishing periodically is SOP.
A true professional at restoring guns can fool even the most trained eye - the restored gun will appear to be 'as original'. I have a friend who restores a truly beat H&H DR and it was assessed by a couple of H&H employees as a great example of the quality of work they turn out. In this case, the restorer has over 40 years experience making old, used guns better.
