The other part of the joke is that Clark Griswold keeps wanting to detour to see every worthless roadside attraction along the way (World’s Largest Mud House or something like that), but has no time for the Gateway Arch in St. Louis or the Grand Canyon.
It has been a long time since I have seen, so I have forgotten a lot about the movie. I haven’t forgotten a young Christy Brinkley however.
World’s Largest Ball of Twine.