Yeah, most schools would cast every single ensemble role as a different actor, plus have non-speaking ensemble for crowd scenes. The style of music lends itself to bigger choreography numbers, as well.
It doesn't matter if the kids don't like the music, being able to say it features songs people might recognize in advertising would help. I mean, the first question I get about any show I music direct for a school is "What songs would I know?" Good or not, full song or significantly truncated, people know "Knock on Wood," "I Am Woman," and "Signed, Sealed, Delivered, I'm Yours."
The concept makes a good sound bite, too, which also helps with marketing. A send up of all the 1970s disaster movies featuring the hits of the 70s. You teach the students variations on that to tell all their family and friends and the word starts to get out there.