Spice is not a MacGuffin! The role of spice in the Dune universe is well defined and shapes it's economy. It's not a side-issue to the plot, it is central to the motivation of the characters and has real effects on the world besides being an object of desire. Spice has a purpose in Dune, it has an actual function in the world. It is a plot device, but it's not a MacGuffin.
Why did someone who cares nothing for science, or for science fiction, review Dune? NChick just comes across as dumb as a brick in this review, "folding space, whatever that is". Dammit woman, watch a show on the Discovery Channel with Michio Kaku or something. Heck, watch a recent episode of Doctor Who Confidential where an astronomer explains the concept of folding space to Karen Gillan. Folding space is not a unique concept to Dune, nor is it even unique to science fiction. It's not a real method of travel, yet, but some physicists think it might be someday.