For starters raise the samples in your AO settings, You'll get a crisper High-res image. Also there is some pinching on your headlights and the little one below it so check your topology in that area.
For your color render the main issue is the image is way to saturated, pic an image to where the ground isn't so blotchy.I also recommend composting your AO on top your diffuse render to get those shadows to make it feel more real.
That's all I can think of right now i'm tired lol, but good job so far, keep at it.
