I'm not concerned about the singing. If I want to see a beautifully sung Sally I can listen to Victoria Clark, Dorothy Collins, Barbara Cook, etc. For the film, I'm just concerned that they get an actress who would be able to truly capture the complexity of the character, if you play her as too needy, too sweet, too much of anything, you'll completely miss the great layers of the part.
I think someone like Amy Adams, for example, could make a great Sally in a good 20 years, but that's the kind of person I'm thinking of. Someone who immediately comes off as vulnerable, but has the range to play different parts of that type of character (I'm specifically thinking of her performances in DOUBT and JUNEBUG).
I think Laura Linney could make a wonderful Sally, though after seeing her in something like NANNY DIARIES one would think she's a more natural fit for Phyllis.
George Clooney, if a bit too predictable, would be pretty good as Ben Stone.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"