Well black is the perfect color for a car, if you ask me.
Just needs some contrast, for instance some indicator lights inside the headlights.
Are you using Brazil? If so then indeed some blurry reflections on the wheels would be nice.
Here's a magic tip that saves loads of render time: put the Max Error in the Adaptive Samplive thingie of the Glossiness Reflection Control of your Brazil Advanced material to 0.15 or 0.2 in stead of the 0.01.
I personally don't really like the roof air scoop, but that is more a designwise comment. Nissan doesn't do rallying... but then again, I suppose this is a streetracer, so I guess it's allowed.