NYC filming and movie tours… worth it?

My daughter (16) and I are going to NYC for three days this week and I was wondering if the TV/Movie tours in the city are at all worth it? Do they walk around the city or take a bus? Do a lot of people usually take them?
Also I wanted to know how to find out where and when tv/movies are being filmed in the city. My daughter is a huge fan of Gossip Girl and would die if we saw them filming!! Please help!

Gossip Girl is filmed at Sivlercup Studios in Long Island City.
I don’t know if they have a tour or not, but I really doubt it.

http://www.silvercupstudios.com/east.htm

Zuzanna Szadkowski, aka Dorota, on the Gossip Girl Tour – On the Bus