My cliff notes of this post : Hubbard was insane.My take is that the L. Ron Hubbard had a fair amount of intelligence, but was fatally spoiled as a child. He grew up vain and lazy. He also grew up good at spinning stories. If you've got those traits, the temptation to live in a fantasy world is very strong.
So I think that in one sense Hubbard genuinely believed in his 'tech', and genuinely wanted to help people with it. But only in the sense that he lived in a fantasy world, in which he was entitled to be worshiped for saving humanity. I'm not sure he really believed in his fantasy with a cold, narrow gaze, the way a hard-nosed investor believes in the business he puts his money into. Maybe it was just a matter of insisting on playing pretend.
I think that a lot of the content of Scientology was probably designed, at least subconsciously, so that Hubbard could maintain his fantasy despite being an intelligent and experienced guy. He really did command a warship, and he really did sell a lot of fiction. It's not easy to live in a fantasy world if you've done those things.
But a fantasy universe of thetans who mock everything up is maybe slick enough to pull it off with. If that's your fantasy, then whenever your common sense starts to kick in, or you start to recognize that you're making stuff up, you can handle the doubt by saying, "Of course I'm mocking it up — I'm Source!" If you keep that juicy thought in the back of your mind, you can quite comfortably laugh and wink about the foolishness of it all, and pretend convincingly that you're not pretending at all. A fantasy about how reality is just fantasy can look reality in the eye and not blink. Or at least seem to. That's how I imagine Hubbard could come across as a down-to-earth guy, when he wanted, and not as the megalomanical cult leader he really was.
Anyway, that's my guess. Scientology is effective at helping people maintain their own delusion, because it was designed to help Hubbard maintain his.