Nice! You have all the work done!
However, I think you need to try some material tweaking and lighting setups. I think you can get much out of the engine than this.
Are the trees casting any shadows? It doesnt seems like that from the renders. (tick CastShadows in the box for the specific vegetation).
I think you should try different TODs and try to make the materials more realistic, and not so flat and neutral. Try different HDR values, as well as turning up SSAO to get more contrast with shadows and sun. For the materials, add a detail bump map, use for example CrazyBump to convert you images to bumpmaps.
Also, try this flowgraph tweak, really nice DOF and color correction. viewtopic.php?f=308&t=71723