Long thread here and I have not reviewed the whole thing, so maybe this is not right for you.
But, when you need a huge complex landscape from the air, and your altitude will not change significantly during your animation, you can dump a still screenshot from Microsoft Flight Simulator X and composite over that, If you're a flight simmer (or have a friend who is).
 
FS-X can also make animations that might be usable.
 
Many users of FS-X buy 3rd party aerial photography based terrains that are very realistic (above 2-3 thousand feet altitude). The best are from "MegaScenery":
 http://www.megascenery.com/

FS-X also has good clouds and the ability to control clouds, sun position, etc.

Heck someone who's good with FS-X could probably start a business creating backdrops for com positing!