In case anyone else has a Boxster that is exposed to road salt in the winter (the previous owner of my car drove it year-round in Chicago), I've found an easy way to rejuvenate your colored crest wheel center caps.  
My crests were VERY faded and had lots of little scratches.  I bought some clear fingernail polish, and gave each crest a single coat.  The red, yellow, and black INSTANTLY showed their deep, full colors again.  I applied another 3-4 coats to protect the crests in the future (after seeing how much a NEW set of colored center caps cost.    

    )
Sorry I didn't get any "before and after" pics.  I was too excited to grab a camera when I saw how the first center cap turned out.  
 Just thought I'd pass this along.   
