Is it possible to have a complex molecule that has such amazing effects that only exists on one planet? Is it possible to have giant worms that I guess they shit it out? Is it possible that interplanetary travel is going to be done only by people who take a drug? How about having to were a suit that will recycle your own sweat and piss to be able to live in the desert? Lame!
In the book, it seems pretty apparent that ‘Spice’ is a metaphor for ‘Oil’. In 1965 it was apparent to the brighter folks that the Arabs had a vital resource greatly under their control; the political, economic, and martial implications of that were part of what Herbert (who admitted to being an admirer of Joe McCarthy) was exploring in the book.
However, until we get to other planets, we won’t really know, will we? It seems the least plausible part of the entire book to me.
There’s also the back story of a war between humans and AI that humans barely won, something that movies have a hard time covering.