Economics have always guided the quality of Broadway musicals, but so has audience demand and the level of "informed" audiences. For instance, it's curious that foreign movies, books, and plays were often adapted into musicals in the Golden age up through the 1980s. More recently, musicals are adapted from movies made within the last 10 years or so.. I think this speaks to the level of "informed" audiences we are now catering to.
What's interesting to me is how in the last several years there have been a number of completely original musicals, musicals not adapted from previously existing source material or subject matter. In the Heights, Next to Normal, Urinetown, Avenue Q, and The Book of Mormon come to mind. Yes, BoM is about Joseph Smith, but it opens the subject up into an original narrative.
How many completely original musicals like those have appeared on Broadway? They are rare, yes? Anyone Can Whistle sticks out in my mind, but honestly I am searching for another....
I think the quality of musicals is continuously uneven and will remain forever so.
With Irma you gotta do something!