What's with the whole obsession in the story's world with spice? I would have liked a little exposition on that subject, it's just left to your imagination if you're not familiar with the books. A psychoactive substance seemed to be the only explanation in the films.
The "audiobook" that Paul is listening to between minutes 6 and 7 in Dune Part 1 tells the audience that the spice has health benefits and allows the space navigators to plot their path, making spice a requisite for space travel and therefor the most important substance in the galaxy. So the exposition was there, I guess you just missed it.