I have had good luck polishing the steel under the plating. It seems like there is enough of the soft metals under the chromium to clean up sometimes. I use a 3m wheel made of "EXL". There isn't much chromium on these after 10+ years outdoors.

Before

asfound2 by barnstormerbikes, on Flickr

After


IMG_3855 by barnstormerbikes, on Flickr