I just came back from seeing Florence Foster Jenkins this afternoon. It was everything everyone has been saying, though I found it more touching than funny (funny though it decidedly was, at moments). But then, though I heard my first FFJ recordings in high school, I've never been able to laugh wholeheartedly at them, because she wasn't in on the joke. (And it is indeed true that such reviews as she received for her handful of public performances were always euphemistically phrased, just as we heard in the movie.) Hugh Grant's portrayal was not only touching and convincing, it was (as far as I can tell from my little reading on the matter) true to history: her second husband was indeed devoted to her in many ways, and tried his best to avoid any public exposure or exploitation of her.
There was a play making the rounds a few years ago called Souvenir -- I saw it in Baltimore. In it, Judy Kaye played Madame Florence, and there was one other actor (/pianist), to play Cosme McMoon. Very effective, and Judy Kaye was splendid as she always is. It used the device of letting us hear her sing as she imagined herself, just once near the end. (In the play, it's the Bach/Gounod "Ave Maria," not "When I Have Sung My Songs.") I wonder if anything was paid to the playwright as a courtesy (even if not legally required); it seems a rather substantial "borrowing."