The thing I really like about Planes is that we learn that WWII happened in the Cars universe. Which means there was a Cars Hitler, a Cars holocaust, a Cars Pacific War, a Cars D-Day, a Cars nuking of Hiroshima and Nagasaki, a Cars Rape of Nanking, a Cars Battle of Iwo Jima...
This leads to so many important questions, like: were the Cars Little Boy and Fat Man nukes sentient? Was it a suicide mission? Are ALL Cars nuclear weapons sentient? Did Tsar Bomba have a personality?
What kind of car was Car Hitler? A VW? A forklift?
Was there a Cars 9/11? Were the planes hijacked, or were the planes themselves radicalized?
I could go on
Edit: I just realized a Cars 9/11 gives a whole new layer of meaning to the phrase "let's roll"