That's really good! I'll give you a tip that helped me. Turn your final gather all the way to draft and your render settings to 16/64. Now do a render and save it. Now open your render settings and press "Process" and select "Material Override". In the none box, choose mental ray material. In the surface, choose ambient occlusion (it's the first option). Now press 8 and turn off your exposure settins, turn off final gather. Now render again. You should have something like this...
AO render
Now open photoshop and load up your two renders. Your "Beauty" pass (full color) should be the lower layer and your AO pass should be above it. Now set your AO render to multiply. Now that will add some realism. Flatten the image and adjust the levels and add some sharpening. Then do a photo filter of orange to about 15 - 25 percent.
I appreciate the tips, and I will try them out for sure. But I must say,this is a scene I have not done. This is from a Jeff Patton tutorial set (some people may remember it). I am studying the tut, to make my own, All I have done is add the BR chevy.
Here is the scene I added cars to. I cloned the car to make a different scene.