Personally I think this is a great little scene. The key to a diorama, as in any model building as I see it, is to create an image, a scene that you yourself want to bring from the "mind's eye" to the public eye. And it matter most what you want, and what you feel about what you develop, moreso than the rest of the world.
As for your scene, I have seen the model railroaders find backdrop photos or paintings and incorporate their tree and rock models very effectively to transition from 3D modelling of scenery to applying right to the backdrop surface for closer items in the image, and then the backdrop image itself. So you would have some foliage and tree material applied right on the surface of the backdrop to give it some perspective transition.
~Aric Fisher
aric_001@hotmail.com