I am so glad you got to see it! I felt the same way ... The scene with Sarah Smith and the Tragedian is my favorite in the entire book, and it was passed over.
I hated that! (They mentioned Sarah, but the way it was presented, you couldn't tell much about her.)
I loved the play, but I love the book ... my husband who had not read the book had no idea what was happening throughout most of the play (although I had told him the gist of it on the way to the theatre). He totally missed what happened with the salamander, and that was one of the scenes that had me nearly in tears. He just couldn't tell from the action what was happening or what it was supposed to represent.
Another couple in our acquaintance went -- the man had read the book a few years back, the wife had not read it -- and they were just confused the entire time.
For me, I loved it, and was very moved by so much of it, but I am quite familiar with the book. I think maybe you have to be, in order to get what's happening.
I think what might help is if they made a movie and could do real special effects, then it would be more obvious what was happening, for people who aren't that familiar with the book. Also they could put Sarah and her scene back in!