..use almost any terrain to create an illusion of distant mountains – it's just a matter of dimensions... pre-programmed by nature – we KNOW that mountains are big.

Thanks for that, very cool mountain model. A mini mountain-range for rendering is a brilliant idea for gorgeous imagery with beautiful sunsets over a mountain range, never thought of that. Still, for my purposes, the sky texture also has some advantages.
1) It does not clutter the plan,
2) the perspective is better if the primary goal is to see which view you get from which window (see also SF Feature requests 668) - even if this may be a bit geeky, I prefer a mediocre view where the bearing (i.e. the navigation term) is as correct as possible.
But clearly the two can be combined, and the mini-model approach is perfect for great renderings.

Sketchup ... a lot of people dislike it.

True, and some for good reasons. But there are very many people who love it too. The 3D warehouse is a testemony to that. Sketchup can, for instance, generate terrain models based on Google Earth data. But the accuracy is insufficient for my purposes.

..create terrains with great accuracy using Photoshop and Vue...

Terrain creation as such is not a great problem. It is the data collation that sucks. Which is why I am curious as to whether the approaches you describe use geo-data (contour lines, elevation points) with a high level of accuracy (< 1m). Google earth data must be around 50m (between contour lines), standard topo maps are often around 20m. However, a decent survey map will have a resolution (< 1m). Now, being able to have a ready-made terrain model of high accuracy would be useful.

ok