That's not how Broadway shows work with regards to Press Performances.
Usually the 4-5 performances before opening night and the 2-3 performances after are for Press People, each performance usually having anywhere from 150-250 comped seats alloted (not just for critics, but for papering purposes to make the crowd as friendly and energetic as possible).
well the long running shows flucuate all the time. I mean one week Beauty and the Beast can be at 95% attendence, and the next week be down to 67%. They're making so much money it doesn't really matter. Plus they know it will always go right back up. Just look at the Producers, that show flucuates so much.
Actually I believe Hairspray is down a bit compared to this time last year. Diana's great but it's a bit much to put the credit for the attendance on her -the entire cast is incredible right now.