"The mind" as opposed to the brain is itself a metaphor. Unless you want to talk about the physical action of chemicals and electrical impulses, you're speaking in metaphors, symbols. Some metaphors help us to understand our motivations and behaviors better, and those are useful -- Freud's ideas are powerful metaphors, Sacks' ideas were as well. Not coincidentally, both are exceptionally good writers.
Some metaphors are weak or absurd, and don't help us understand anything. Hubbard's ideas are lazy and derivative of work he didn't understand, and, not coincidentally, he was a dreadful writer.
There is no "grain of truth" in Dianetics or Scientology. Hubbard was a loquacious idiot with delusions of grandeur.
This is why I urge people who are out of Scientology to read good books: Plato, Montaigne, Freud, anything that's stood the test of time. Not because they're right, or even "workable": that's something Hubbard taught you to expect from philosophical or speculative works, and it's something that every intelligent person knows is a ridiculous expectation. They continue to be read because of the strength and originality of their vision, and the grace with which they communicate it.
A great thinker gives you possibilities, not absolute solutions. Ideas, not techniques. One who does the latter is either intellectually dishonest or fascistic.
It's my conviction that anyone reading the work of a really great writer (in fiction or nonfiction) can only come to see Hubbard for the pathetically inadequate thinker he was. If they can't, they may well be lost causes.
Although I disagree about the mind and the brain being the same thing.
The Anabaptist Jacques