I must admit that in the past I was of the impression that Silver cars weren't all that rewarding to polish. But after spending a bit of time late last year going over the CLK after I bought it (and since polishing another silver MB), it's surprising the overall difference once the paint has been thoroughly decontaminated/polished/waxed. It sparkles much better in the sun, the metallic particles are more 'obvious', and the shine/reflection is noticably improved. You'll see less swirling under strong sun/artificial light (eg petrol stations), although not as much of an issue as with darker colours.
I would have to agree with Chrishazle . Machine polishers can give some great results , but too much pressure on corners/angles can get you back to primer or bare metal with alarming ease ( yes , even on a merc ! ). And a small speck of grit picked up on the pad produces some fine artwork. Any bodyshop should be able to give a machine polish to a clean car , for a reasonable price.