Quote - i'm still learning Vue6 Infinite but i find that when i use some simple tricks using clouds, haze, fog and light combinations and by adding Geo Control and Chipps TerraPak  you  can make some realistic scenes.
the basics are fairly easy to pick up but getting into the advance part takes a bit of time i'm finding but i find the more you experiment the faster it sinks in.

you can find some free tutorials at the geeksatplay website.

i'm not familiar with Terregen so i can't comment on it.

Just browse the Terragen section here on Renderosity.
Most pictures there are now from TerraGen2 Tech Preview

It looks and certainly is a generation ahead of Vue in it's technology, but heck it's problematic. It is reported to have render errors, yet no rendertime estimation and the worst no dualcore support.
Atleast till then I better keep my fingers off that, but it's probably going to replace Vue for  pure landscape rendering once it is a bit more towards "beta"

Your Lost River Pic has a good atmosphere I see :-)