I finally found the time to finish a project I'd started a while ago. The still image shows an environment modelled and textured in Blender and rendered in Vray Standalone Beta (using Andrey Izrantsev's script).
The animation (see link below) shows a slightly simpler version of the scene, cut in several layers and projected back onto the scene's original geometry using camera projection. The ships and exhaust heat were rendered separately in Blender's internal render engine.
The animation also shows a mountain landscape animation based on the same idea. For this, I rendered a basic landscape in Terragen and projected it onto relatively simple geometry in Blender for the animation.
This is not perfect, of course. I had some compositing problems with the ships and the camera projection method only allows a very limited amount of camera movement in the scene (any suggestion much welcome).

Link to the 40mb .mov animation: http://www.bertrand-benoit.com/images/MatteAnim.mov

EDIT: City scene vaguely inspired by a scene in the latest Star Trek feature.