Spud's head shape is modeled after Bart's head.
The carnival was based on The Eastern States Exposition (currently known as The Big E) fair. As a child, Mike Scully went to the fair, and had hoped one day to be a carny.
The Rich Texan's line about Hitler's car being the first car with "Fahrvergnügen" was originally supposed to be "...and it was the first car to be featured in Disney's Electric Light Parade." According to commentary, the show's legal team begged them not to use that line, despite allowing every other joke that made fun of Disney in the past. The original line appeared in the closed captions on TV (save for the syndicated version, the international versions, and the DVD version).
This is the only episode that Mark Kirkland told his parents not to watch, due to Bart's line "Out of my way, I'm Hitler". Kirkland's stepfather was a lieutenant in World War II and was injured while in combat.
Matt Groening said that they had several endings worked out, including one where Homer made the hula hoop over the chimney.