I think that it really boils down to whether someone's work degrades the gun. For me, it is fine to lap the bore or reregulate a rifle that doesn't shoot to point of aim. If the bore is completely shot out, perhaps the rifle could be rebored and rechambered to a cartridge that the rifle would have normally been chambered for.
I have seen some refinished guns that the owner would have been better not refinishing or have someone else do the work becauise the colors are garish (way to bright).
Lee Shaver (gunshith and publisher, SSE) said that he doesn't refinish guns to look like they just were produced but like they have some minor wear. I saw a gun he refinsihed and it looked very nice.