Quote - "It is quite ironic that having the supposed most realistic scenery program on the market (Vue) one has to invest in another software - while the best landscapes I've seen have been done with a freeware-ish!"

I completely disagree with this point of view. First, you are mixing two completely different things. The "best" is not necessarily the most photorealistic. "Best" should also measure the diversity, for example. Terragen has more photorealistic renders only in a very specific niche of landscapes. Terragen is only more photorealistic than Vue in what regards mountain-scapes and desert-like landscapes. Real landscapes are much more than this.

Try to make a jungle landscape in Terragen, for example, and compare with Vue. Vue is much better, in all aspects (including photorealism). Everything that has complex ecosystems of plants is more realistic in Vue.
Try to include in Terragen human constructions, like a city-scape or similar. Vue is better.
Try to make a rough ocean in Terragen and Vue and compare.
Try to make a stormy cloudscape in Vue and Terragen.
Etc, etc, etc.

I tell you quite frankly. After seeing 20 Terragen landscapes, I'm fed up and want to see something else, because everything seems repetitive after a while (mountains, deserts, etc). After seeing 20 Vue landscapes, I want to see more and more because the diversity never ends.

Quote - "What concerns me though is that I can't seem to find hyper-realistic renders of Vue anywhere! They all look like illustrations, while what I am trying to do is to make "photographs". "

Then use Terragen, not Vue. You should use whatever software is adequate for your needs. Why "fight" with Vue to get the results of Terragen if what you really want is Terragen?

Quote - "I only softened the sun shadows 20% because I don't like hard shadows."

Then, how come you like Terragen renders? Are there soft shadows there? I don't remember seeing a TG render with soft shadows. But maybe there are.

Quote - "I will give Geocontrol a thought. I visited the website but couldn't understand what that program really does"

It creates terrains. Nothing more, nothing less. And does it very well. You have infinite possibilities. You can define all types of erosions, rivers, lakes, etc. You can export a heightfield from GC to Vue and use it to define a terrain there.