The play itself is reason enough to go, along with Gugino. It's something that's rarely done, and we won't see another professional production in New York for a long, long, long time.
If you haven't seen this yet, please do go. Gugino is superb. Tickets are extremely hard to come by, but try cancellation or something.
There is also a pending extension (past the current 1/14 closing date). They are waiting on Danner and Gugino's agents' approval. Hopefully after the raves for Gugino, they will go ahead with it.
"If you are going to do something, do it well. And leave something witchy."
-Charlie Manson