The first is that it's a terrific, vibrant performance -- indeed LuPone won the Tony Award that year for Best Actress in a Musical. And the second, mainly, is a reason I've mentioned here in the past, and used a clip of the movie version with Rosalind Russell as evidence. This live, stage version confirms that.
I suspect that most people think of the song, "Everything"s Coming Up Roses" -- written by Jule Styne and Stephen Sondheim -- as an uplifting anthem of unbridled optimism and succeeding against all odds. In fact, in the show, it's actually about manic self-delusion.
At this point in the musical, the star of the little, ragtag group's failing act, June -- who is Mama Rose's youngest daughter -- has just run off with one of the act's dancers and gotten married. Since that appears to put an end to the act, Rose's oldest daughter Louise is actually overjoyed, as is Herbie, the group's manager and Mama Rose's boyfriend. After all, Louise knows that she herself has no talent and is unhappy on the road and just wants to have a normal life and a stable home. Herbie knows that the act has been getting continually less-successful and once they give it up, he and Rose can settle down and get married. But to the obsessive, driven Mama Rose, living her life through her children with a deep, desperate, personal need for stardom, she instead blocks out reality and decides she will rebuild the act, and that it will be better than ever. As she sings the song, it's not to inspire the others -- in fact, you can seem them horrified at her madness -- Louise (played here by Laura Benanti, who most earlier this year starred as 'Eliza Doolittle' in the revival of My Fair Lady) and Herbie (played by Boyd Gaines) hold one another tight in despair and almost self-preservation, watching helpless as Rose ignores them and sings only to herself.
This is not an uplifting anthem of plucky can-do spirit. This is how it goes --