If you haven't seen the unsold series pilot we mentioned on the podcast but plan to or don't want the cast spoiled, please watch it now. One of the great joys of seeing it is going in unknowing and enjoying who they did get for that version and who they did not. This list considers performers in the TV pilot part of the High School USA universe and ineligible for ranking.
1) Anson Williams: I believe that a certain cosmic singularity would be reached by having a star of a 1970s show set in the 1950s appear in a 1980s movie set in the 1980s but featuring 1950s/1960s-tinged music. And I believe that star should have been Anson Williams. He could be the cool older brother of one of the students, a sibling who just happens to be asked to sing at an event--maybe the climactic Fox/Edwards race!
2) Gary Coleman: You could argue that he was too "big" for this in 1983, and I could counterargue that that's a cheap height joke and you can get right outta here with any suggestion Gary couldn't have fit in with this movie!
3) Kathy Garver: The Family Affair star is fresh on my mind after our Spider-Man and His Amazing Friends episode this season. She could have been a young teacher--you know, one not hit on by a hapless Dwayne Hickman.
4) John Astin: High School USA spotlights many stars of vintage family sitcoms. Maybe The Addams Family is a different kind of family sitcom, but it's a family sitcom nevertheless, and Astin could have added some unforced (I hope) wackiness on the faculty side.
5) Dolph Sweet: Should have been in there as a policeman who at first seemed to menace Michael J. Fox and the misfits but ended up threatening to pummel Anthony Edwards and the preppies.
6) Philip McKeon: We got his sister, but where is her bro? He could have fit in on either side in the misfits/preppies conflict.
7) Valerie Bertinelli: Maybe you think she was too old to play a high school student in 1983, but she was a year younger than Cathy Silvers. One Day at a Time was still on the air at this point.
8) Karen Valentine: Who couldn't use more Karen Valentine?
9) Danny Thomas: He could have been the school superintendent or some kind of elder statesman in the Sid Ceasar/Milton Berle role of "comedy legend who is here for no apparent reason than just to have a comedy legend."
10) Warren Beatty: Well, he WAS on Dobie Gillis! It would be funny if Beatty played a preppy heel student--yes, in 1983--who walked off with all the girls running after him.