OK, first off, I really love this image. I think you chose well as your inspiration from that painting you mentioned & shared. That said, I actually enjoy your image MORE than that initial inspiration.
In your image, you have made everything more immediate to me as the viewer. I can instantly relate to the actual tagging, the decrepit foreground elements and that gorgeous car.
As you look into the image, you've captured our sight lines very well and the interplay between light and shadow does an excellent job of highlighting where our eyes need to be looking. I found it particularly interesting that as you move back towards the more high tech city, that the styling becomes more an more limited, that maybe going in that direction you are sacrificing creativity. That idea immediately slamming the viewer in the face with that colorful and beautiful graffiti!
I think (and this is a nitpick) that the elevated Train might work better as a sleek counter-grav train -- shiny but muted in colors, again to showcase that difference between now and the future -- plus it would help emphasize that dividing line. If you want a nod towards a more fully sci-fi look, a small helper bot holding the paint supplies for our presumed tagger
Again -- I really love this piece. Well done indeed!