is this lit with one of Guthrie's hdri's? if so, i would try lowering gamma to 1.8 instead of default 2.2
it may help get more global illumination contrast.
emitter illumination looks good, but the global illumination is causing everything to blend in together. i think either lowering your gamma in the render or the hdri itself while boosting the ibl value may help give the building and environment a little more "pop"
edit: i would opt for geometry for trees and vegetation vs. billboard. given the mood you're going for, i would place a small emitter pointing up at base of each tree for added effect. i think these little things would make client happy
