My Boxster's shift knob looked much like yours when I got it so refinishing it was one of my first projects. I didn't want to repaint the chipped plastic bit because I thought that rattle can spray would be even less durable than the OEM finish so instead removed all the original silver paint and polished the black plastic beneath. It came out pretty well I think...
If you do decide to paint, Testors #1830 "Diamond Dust" paint is a good but not perfect match to the Bosxter's "titanium" interior trim. I've used it on my car and like the result.
Even though my refinished knob was a big improvement I eventually replaced it with a walnut knob that I made, an even greater improvement in my opinion!
Cheers- dj
