"Hair was huge in its day, but its effect on the artform was brief. Despite numerous attempts to copy it, none of the other rock musicals or events had even a small share of its success."
Hair's effect was quite far from brief. It was the first show with a true rock sound to become a major hit and its success led the way for dozens of rock musicals since (some that were more successful than Hair itself) -- from Jesus Christ Superstar to Godspell to Pippin to Tommy to Dreamgirls to Rent. Hair is one of the most influential shows and scores ever written.
"I don't think you can say a show redefined theatre based solely on attempts to copy it (as some have done in this thread, citing BKLYN)."
But that's what influential means. And no, Mammia Mia isn't a work of art, but it is the most INFLUENTIAL shows of the past decade. Because of its massive worldwide success (over a billion dollars of ticket sales), Broadway producers have been frantically running around pursuing to the rights to the rock/pop/r&b music catalogue of every known and not-so-known artist of the past 50 years. Mamma Mia is directly responsible for DOZENS of shows that have played here or in the West End or are in development (Jersey Boys, Look of Love, Lennon, All Shook Up, Good Vibrations, Hot Feet, Ring of Fire, Our House, We Will Rock You, The Times They Are A-Changin', The Wall etc....). Now, has Mamma Mia's influence been a good thing for theatre? That's another question entirely.
"What a story........ everything but the bloodhounds snappin' at her rear end." -- Birdie
[http://margochanning.broadwayworld.com/]
"The Devil Be Hittin' Me" -- Whitney