Simulating car duco is a particularly difficult thing to do, if you are after ultra realism. The problem is that modern automotive paint surfaces are very complex, usually with a clear coat over a flat or metallic base colour, and if you don't at least try to replicate this you'll end up with a plastic look.
I have attached my best attempt at this, which still falls short of the mark. In this image there are two objects making up the fender: a base model with a blue paint material, and; an upper model with a clear material that simulates a clear lacquer.
The material specifications are: -
Blue duco:
Ambient=.3
Diffuse=.7
(colour for both 2,64,180)
Specular=.6 (colour white)
Emissive=0
Rough=15
Brilliance=1
Trans=1
Attached 'OrangePeel' texture applied to Bumpmap, value=15
Clear lacquer:
Ambient=.3
Diffuse=.7
(colour for both 245,241,228)
Specular=.3 (colour white)
Emissive=0
Rough=1000
Brilliance=1
Trans=0.1
ART attribute: specular, value reflection.
So, the blue underlayer is flat with no ART reflection attributes, but provides a light bump simulating the sprayed-on appearance of paint (the UV map of the fender was adjusted so the bump map was very small, providing a light grain). The upper reflective layer is providing the actual reflection, which is unaffected by the bump since it is applied to the outer model layer.
I don't know whether you'd be happy with this method, it might be problematic on a full car body (for instance, you'd most likely want to map the UV coords of the grain texture so it doesn't stretch anywhere). You might also have some luck with the Glossyreflector attribute (which was used to create the rough, silver metal on the wheel rim, from where the valve protrudes).