So here's a look at my gameboard with some of my terrain items placed on it:
And from another angle:
Here I've moved the camera position closer to the board, and turned on "shadows":
And finally, a miniature's view from the big mountain, with distance "fogging" turned on:
Based on a few hours of experimentation (and no previous 3D design experience!), it looks to me like SketchUp has some promise for designing scenario maps.