You know, if you read Belthasar's journal in which he says...
"It all began aeons ago, when man's ancestors picked up a shard of a strange red rock... Its power, which was beyond human comprehension, cultivated dreams... In turn, love and hate were born... Only time will see how it all ends."
... dreamstone seems to serve the same purpose as the forbidden fruit in the Creation Stories. It created a higher level of thought beyond instinct, thus elevating humans from other animals. Just like Adam and Eve developed "knowledge" and realized they were naked and so on.
And it also seems to function as the Eastern god(s) do. If you listen to Alan Watts explain that God dreams the world into being, and we're all a part of him/it/whatever... Dreamstone (thus the name?) appears to cause something similar.
Or maybe (and now we're getting deep) the "cultivation of dreams" simply means it brings out the potential within us as a species. We seem to generate and grapple with ideas in dreams first. Freud and Jung talk about this to levels I'm not qualified to explain. But it's in dreaming that the mind will confront problems. And dreaming, really, is the mind imagining things. Maybe imagining them uninhibited.
Think about this: we're different from animals because we can imagine the world and our actions as possibilities without experiencing them. We can reason out the best course of action without having seen it before. This is, in a sense, dreaming. So you could say, in the context of CT, that dreamstone is what gave humans this ability, and thus elevated us above the rest. (Which ties back into the forbidden fruit of knowledge, concepts like love and hate being born, on and on.)
