You have to wait until a movie opens in wide release to see how it really does. And remember that the per screen take for the Producers was considered 'solid' by Variety in select city openings, so these movies are far from doomed.
However, movie musicals like RENT and the Producers will not have WIDE appeal in the U.S. outside of larger cities as they are not mainstream, family movies or big action films.
So you do have to keep your expectations in check. They may make up for a lot in international and DVD release and at the end of the day...it is the total take that studios will consider.
I don't think you can include MATTRESS in your consideration because made-for-TV musicals are a whole different thing.
"Life is a lesson in humility"