this might sound dumb, but i would crop a little off the right side. you can see the bricks from the vertical part of the arch on the right side, but not the left. little things like that really help to frame a picture.
one thing that i would definitely do is bring down the highlights on those guys in the front some more - not a global highlight reduction.
also, increase the definition just a tad. its very similar to the clarity slider in LightRoom, and they both really add "sharpness" and make the picture pop.
other things that i would to, which are of course to taste, would be to add a vignette.
also, a great trick i learned for aperture that sometimes looks amazing is this:
go to color monochrome - pick the crayon box - select mercury - take it down to 5% opacity in the color selector (not the adjustment pane) - finally, go to the adjustment pane and drag it pretty far down until you find something you like.
all in all it's a nice pic. pretty even exposure and everyone looks interesting.