Marin Mazzie (my favorite Broadway actress of all time) needs a wild and crazy musical comedy role, and Judy needs a layered, complex, R&H-esque role. While both are incredibly versatile and have succeeded in the polar opposites of what I've suggested, I have found these to be their strengths.
Maybe Marin in a new Shaiman & Wittman musical directed by Casey Nicholaw and Judy in a new Adam Guettel musical directed by Sam Gold.
I'd love to see Marin as Mama Rose or Norma Desmond, and Judy as Cinderella's fairy godmother or Genevieve in Schwartz's The Baker's Wife.