The oil analogy is important but it's not what the whole thing is about:

I wrote the Dune series because I had this idea that charismatic leaders ought to come with a warning label on their forehead: "May be dangerous to your health." One of the most dangerous presidents we had in this century was John Kennedy because people said "Yes Sir Mr. Charismatic Leader what do we do next?" and we wound up in Vietnam. And I think probably the most valuable president of this century was Richard Nixon. Because he taught us to distrust government and he did it by example. -frank Herbert

It's a warning about putting faith in charismatic leaders and personal dogmas, the oil/spice analogy is good and important but it's not the main point of the series.