I have quite a few machines that show years and years of cosmetic wear from use. Unless the machine is badly rusted like my New Home AB I just clean them good and use them. I hate to paint them because that destroys their history.
Some will say that wipes the slate clean and you can make your own history then, but none of us will live long enough to put much wear back on these machines. Most of them have already been in use longer than we've been alive.
Joe