Definitely nostalgic adults, I would say. With its teenagers burdened by heavy responsibilities, the show conforms to a line Slate's founding editor, Michael Kinsley, once used to describe Al Gore: "an old person's idea of a young person." One fan, Ruth Samuelson, wrote to say she interviewed football players from the school where the show was originally shot. They were all pretty lukewarm about the show and preferred MTV's Two-A-Days. Also, FNL is apparently one of the most popular among "affluent viewers," which can't be teenagers.
That said, I love your point, Meghan, about Shelby/Sunny—that she is an orphan's fantasy of a mother. This would explain her flatness, her angelic nature, and Matt's near-muteness. It would also attribute to the show a genuine child's-eye view.
One thought I had reading your descriptions of Mindy and Tyra: For the first time, Tyra fails where Mindy succeeds. Tyra is a victim in that skeevy dive of a bar, the terrified object of threatening male attention. Mindy, meanwhile, is using the skeevy bar as the source of her feminist liberation.
Now, all you die-hard fans, check out these rumors of two more seasons, and begin to ask yourselves the relevant questions: Can Tyra, Riggins, and Lyla all flunk senior year? Can they really shoot half of the next season in San Antonio, where Riggins apparently will be? Is J.D. man enough to inherit the drama?