My impression was that melange or "spice" was a metaphor for oil, which is mostly controlled in the desert regions of our world and which also controls transportation and therefore commerce (as does spice). It is symbolic of any monopoly that controls everything indirectly. But the spice metaphor goes further than that, with the life-cycle of of the worm from which the spice is made, and its religious implications (which do not exist with oil, but the Middle East is full of religious fanaticism based in dry desert-thinking). Also that it makes its practitioners clairvoyant so they may navigate — and also makes them addicted — has many different implications. There is a lot of bending space and time going on in our environment. And much in the way of hegemonic rule, which the Dune series is all about.