I, too, go to advanced screenings all the time. As for movie musicals, I attended adv. screenings of Rent, The Producers, The Phantom of the Opera, and Dreamgirls. Sometimes there is swag that you'll receive from the regional sponsors (radio stations, tv stations, or local companies). Never ever ever have I not gotten in with my passes. Never have I seen people get rejected...even if the screening was at capacity. Never have I seen fights over swag.
Generally, the people running the screenings (in terms of who gets seats and swag) know what they are doing. The actual theatre that hosts the event just do what they are instructed to do. Sounds like to me that there was an overbooking and the e-vites didn't have a "cap" limit. It does sound right that the "hair salon" folks got to go in first.
"The Spectacle has, indeed, an emotional attraction of its own, but, of all the parts, it is the least artistic, and connected least with the art of poetry. For the power of Tragedy, we may be sure, is felt even apart from representation and actors. Besides, the production of spectacular effects depends more on the art of the stage machinist than on that of the poet."
--Aristotle