The Major's right, of course. As a general rule, refinishing a gun will hurt its collector value and that's for you to care about or not. Personally, if I had one that was perfect for my persona and it needed to look new(er) to fit, then I'd go ahead and do it.
Then there are the ones that would probably be made more valuable with a new finish, like my holster-worn Ruger Single Six, but I like the character it has so I won't refinish it.