Some interesting thoughts there on the Brackett script and Lynch's Dune.
The sequences you talk about in Dune aren't mystical as such, they are altered states of consciousness and there is isn't much of that in Star Wars.
Paul sees the melting hand because of suggestion backed up by nerve induction, nothing particularly mystical about that.
He sees the golden path because of, 'essentially' a massive drug overdose which he is trying to control using physical and mental discipline.
The Bene Gesserit dress it up as mystical because it gains them political influence.
In the OT there is no drug that makes the Force happen, life makes it grow not the Spice, only in the PT do you get any form of in universe mechanism for Jedi/Sith ability (ROTJ introduced the notion that blood lineage is a vector but until then anyone could be a Jedi, that was the charm of the idea).
It took generations of selective breeding, Spice saturation and training to produce one Kwisatz Haderach.
So the OT approach is even more of a cinematic achievement because that space opera had real mysticism where as Herbert's had rationally described phenomena resembling the mystical from book 1.
In a way it would have made more sense to flip the styles around and yet counter-intuitively I think they both worked better they way they turned out.
Lynch's Dune isn't a faithful adaptation of the book but it's cinematically evocative of the sweep of the book in a way that a purely physical adaptation couldn't have been.
I'm more shocked that Lucas went for Brackett and Lynch (as a choice to direct ROTJ) in the first place.
If you read her books, her script is very much in her style and Lynch's work should have flagged up how difficult to manipulate predictably he is and that was clearly not the sort of director Lucas wanted.
Lynch had Lucas summed up when he met him.
His suggestion that George direct ROTJ himself makes me wonder if he hadn't been swimming in spice gas himself.
It's a shame in a way because if he could have survived through to the end a Lynch ROTJ might have been a better film than the 'Lucas by proxy' film we ended up with.
It might have also have been less painful for Lynch than having his planned adaptation of the Dune saga snatched away by Dino.