Yes the car sex one. What was the point of that?
Ballard's book is one of the most respected and influential in the entire genre. His intro to the French edition is (I think) one of the key philosophical texts of the last fifty years. It's an essential media critique.
As for the movie, it does a good job of relaying the story and themes of the book, but doesn't have the same impact since the book is written in a radical style (specifically, in the manner of what Ballard would call the hidden literature of medical and scientific texts).
Ballard's value, I think, is the way he exposes narratives and environments that we choose to elide over because they're not part of the media driven story we're participating in. In Crash he's particularly interested in how we've elided over, or folded in, the amount of death inherent to freeway travel. If that many people died because of war or disaster it would be a central cultural focus, but because we've institutionalized it then it becomes invisible. But it still exists and then we fetishize that death and damage.
But he's also interested in the ignored landscapes of access roads and loading docks and airport hospital wings which stand empty but ready to receive hundreds of victims at a time. This world that our eyes pass over without ever taking in.