nice job
i had some idea's / pointers / thoughts looking at the chop maybe you can use it ? >>
,i think the taillights look to desaturated , you should have left the already white / grey top part as it was and then get rid of the red , but even then it needed some hue from the surroundings .
that way the lights really would look that much better
bg idea is cool i think i would have tried to show a bit of the new bg trhough the windows , also something that would add depth and a fresh look
the last thing (sorry for whining

) i think if you changed the sky colors for normal realistic colors (or toned down the red and purples a bit) and used that to give the rest (read car and surface in front) a color filter it would all come together as one