Think of it as a real photo. If it was, what would you do to improve it? Well, for starters, I would fix the black point, increase / adjust contrast, increase the structure (ie, large R USM, or equivalent), add suggestions of more complex colored lighting gradients, a slight vignette, maybe add a tiny bit of grain, etc. These efx are shown in attachment #2.
I would also get rid of the faint horizon line that unintentionally extends through the building. (Unfortunately, I didn't have time to do this.)
As a final step, I would drop in a real background on the RHS.
In other words, do everything R-M suggested + more. ;-)
Just my $0.02,
#1 = the original, just down-rez'ed for easy comparison to the other images
#2 = making it more photo-like
#3 = adding a real background on the RHS