ok some pointers:

the trick is with vectors is you have to know when its best to use a flat colour and whento use subtle gradients (gradients are still vectors dont forget... sort of...) anyway, on your piece some SUBTLE gradients would go amis, especially on the red parts of the car behind the steering.

with vectors you can always add in highlights and some extra stuff in photoshop (like meaty did) if done well the results can be fastastic

if you neatened up the lines it would be a lot smoother and the picture would flow together (especially around the horn logo thing)

its a really good piece for your first vector though well done

oh and dont keep sampling colours. if you have two areas where they are basically the same colour it looks better to just colour both the same than if you have slightly different colours for both (again like the red bits)

ok i made a version of your picture showing what i mean. I hope this helps!

These pictures are so cool, I wish someday I will be good enough to make one of these. Good job, everyone.