I used Griots plastic polish and a micro fiber rag. If you don't have anything to deep.
It will come out looking like new! Then use you some vinyl dressing thats not to greasy (Adams VRT works great)

 

I weld iron when working on cars and I weld plastic when I ride my crotch rocket. If you think Porsche parts are expensive, just wait until you drop your sports bike and try to buy the plastic fairing.

With those prices, one learns to manipulate plastic.

 

Great job and much appreciated for sharing.

 

For those who might want the paint route, consider the paint made for plastic/bumper. Unlike regular paint, this paint is somewhat flexible and a lot less prone to chipping or cracking when bumped.

Note that painting will not hide deep scratches.

 

Look in the Rennlist Forum in the 997 DIY. Search... refurbish door sill/ scuff plate. An excellent DIY with amazing results.

 

Well, Crazycarlitos beat you to it (see post #3).