Hi Bogey,
I think for the scene you had here, there isn't much indirect lighting needed, because you already have strong light source from above and there isn't many objects (or any at all) for lights to bounce back to the car, if the car is in a large studio room then the chances for the light to bounce back is very minial. You could have lower your G.I. setting and probably still get the same result. (sorry I am not a blender user, but I think you are enable to do so)
I used to use 'light tracer' in 3ds max before, the result is very good and accurate, but it took many hours to render an image, I think that is simular to Indigo in this case. However, I have no patient in waiting, I am using Mental Ray (using Photons) more often now for still images.