I think it looks very nice with the aero kit installed. I'd up in the air though. It would look very nice with the black bumper covers and wheel wheels painted to match.

Then again, your contrast would be gone and one might not notice the aero kit.

I'd be inclined to leave it as is, simply because it's already extremely nice. That is to say, I'm not sure it would add anything to the car, and it might take away from some of what's making the vehicle look "aggressive and sport," which to me is the contrast.

Sometimes painting everything silver, with the aero kit, makes an X5 look like an X3, which is arguably more sporty in appearance, but it's just not as classy.