I'm playing Man of LaMancha this week here. I made my summer money one year playing this show (I think we did well over 30 performances). There's quite a lot of music theory examples to be had in the show.
Modal mixture: "Man of LaMancha," "It's all the same,"
Hemiola: "It's all the same," "Dulcinea," "I'm only thinking of him"
Asymmetrical meter: "The enchanter" (7/4); "What does he want from me?" (7/8); "Golden helmet of Mambrino" (10/8 as 3+3+2+2);
Alternating time signatures: there are many of these (6/8 & 3/4); most interesting is "The Combat," which alternates between 6/8 and 7/8.
Truck Driver's Gear Change or the "One more time" technique: "Aldonza," "Fight sequence," "Finale"
Whole-tone scales: "The Combat" begins with whole-tone scales in the bass, which are then filled in with chromatic steps in the upper voices.
Bitonality: "The abduction" has "Little bird, little bird" in G major simultaneously with some G-ish modal interjections
Horrendous key signatures:"It's all the same" is in A-flat minor!