Anybody know the best procedure to repair small paint nicks for a car with metallic paint & clearcoat finish? I have the Mercedes touch-up paint, but is there anything I should do to make the repair less noticeable?

This would be better addressed to the detailing forum but since I'm already here...
The "kit" of colored basecoat and clearcoat is a great place to start. For near transparency there are two methods for touchups practical to the non professional. If you don't want to have to buff/wet sand/etc when your done with the paint you can try building it up in layers. Strip/deep clean the area being touched-up, and apply the paint in as small an increments as you can. Let dry for many hours and repeat. Even if you stretch it over a week or more you will get the desired effect if your patint and don't just "slop it on". Of course there is always the slop and sand method but I would avoid that if possible. Or just slop and leave it...being about the same. The other method I would recommend is the use of a ultra-tiny diabetic syringe. The model I use has a 1cc capacity and a needle that is about 3/4 of an inch long and ultra-ultra thin. Suck up the paint and inject it into the chip. Let dry and clearcoat with similar method. I have seen pros use something resembling an airbrush on stonechips and key-scratches but that isn't available to most of us. When the pro was done the only indication was a slight difference in the orange peel or reflectivity under perfect lighting conditions. Best of luck on a very annoying problem...Lee