You are getting lots of advice concerning white balance, but as I understand the original post, you are happy with the colours you're getting. The biggest problem with the 2nd and 3rd pictures you posted is that they're out of focus (check the distant houses on shot 3 - they're sharper than the car is). The second problem is that they're slightly under-exposed, and the third is I think there is still some movement blur on top of the out-of-focus blur (the 400D should produce much crisper pictures than these). Is your tripod up to the job, or do you not have a remote release?
Putting bright light sources in the frame can add impact, but will throw the camera's light meter into thinking there is more light in the scene, hence under-exposing the subject part (your car). They also give your lens a stern test when it comes to flare, which you have here. Did you have a filter on the lens? Removing it can help in scenes like this. A little flare is to be expected in such a scene and can even add a little impact too, but it has led (along with under-exposure) to reduced contrast - the 'flat' feeling the pictures have.
Don't give up! You don't say what lens you're using, but I think you need a wider angle, taken from a close perspective, like in the 2nd shot, but getting more in. Use lower ISO, smaller aperture, and longer exposure, with a solid tripod, maybe focus manually. Try longer exposures than you expect to need and see how they turn out. The beauty of digital is you can check immediately. Don't forget even flat originals can be improved in post-processing (better to start with the best you can get in-camera though). Keep trying and post up your next lot, which should be better. 
