Jani,
I would agree about the bluing if the gun was an unmolested historical piece. It is post war, has had 2 scopes mounted ( so it has already been blued at least once). The owner seems to intend to use it regularly, so bluing it won't detract from any "collector value". "Collectors" will turn up their noses at it if it is blued and will turn up their noses, if it is not blued. Since it doesn't seem to be for sale, it wouldn't make much difference to anyone except the owner.
Mike