From what I gathered from my source, the role of Clara Johnson was changing in a lot of different ways from the Chicago production. They didn't want her disorder to be so bluntly acted out the way Celia portrayed it. They wanted Clara to be a little less absent-minded and a little more "youthful" (like what I've been hearing Katie Clarke brings to the role).
Reason being, the audience could relate more and you could really buy into the idea that "At first, the Naccarellis dont see anything wrong with Clara. They just think she's a stereotypical YOUNG, American, endearing, silly girl."
I saw Patti in the role of Margaret. She was different, but I liked her better as Signora Naccarelli. I found her Margaret to be more motherly and maternal than Vicki's. She was a lot more cliche' "affectionate, suburban, overly protective". I liked that a lot about her performance. It was something I wouldn't have expected from Margaret, but ended up enjoying.
Bill Finn rocks. Woot.