I'm always trying to explain to people the existence of "theme cars" that I was use to seeing in Hampton Roads growing up. This is an example of a theme car subtype, the shit glued on it. https://twitter.com/cryb0i/status/1349878301339344896
Another major subtype is "custom paint job." This is usually of a beloved media, like the SpongeBob car shown here. There was a very similar one driving around Hampton I would see frequently.
I would not consider "too many bumperstickers" a theme car subtype, unless all bumper stickers follow a salient trend. Schizophrenic religious words are an example of this.