Riverdance was excellent. I didn't see Stomp. I want too.
I am not sure about the backstage tour. It really depends on where you are, and what is playing, and who is in the show like if it is a major actor or actress. I would give anything a try at least once. What can it hurt? Really.
Now, with all the terrorist things going on I am not sure in NYC. But again, give it a whirl.