Lisa E writes in comments on the last post:
OK, here's my impresaria fantasy:
There are many places to workshop a straight play: Long Wharf, Eugene Oneil, Actors Theater of Louisville, Playwright's Horizons, et al. To my knowledge, there's no good place to workshop musicals. I suspect that many would-be musical writers/composers work in other genres (Fringe Festivals, etc) because they have no venue to create a "real" musical.
What if you had a one-month workshop where a group of selected musical writer/composers could workshop their shows? You could have an agreement with an orchestra that's in its "dark" season, and audition a group of actors/singers, who would work on multiple shows. THe chance to hear your words sung by real singers, accompanied by a real orchestra, would be an amazing thing for show creators.
As Alex noted, the Fantasticks didn't require anything fancy -- it actually started as a summer theater project at Barnard College. I saw A Chorus Line at the Public Theater -- it was a nearly blank stage, with some dancers in leotards. We think of Andrew Lloyd Webber as being the creator of overly lavish productions, but his first hit -- Jesus Christ Superstar -- had minimal technical requirements; you could do it on a blank stage and it would still be great.
I think that if writers/composers had a reasonable chance of mounting their shows, we'd see a lot more creativity in the genre.