If it were to letter as one of the few 28s that were originally made in nickel, value will be enhanced. S&W had a strict policy for many decades of not offering a change of finish from blue to nickel on the Model 28, although I believe they will now do any finish they offer for a carbon gun on a Model 28. Factory refinish will not generally harm value, although an all original finish in great condition will still be worth more than a factory refinish. A non-factory finish, on the other hand, will detract from value.