I've always been under the impression that kids were not welcome in the specialty restaurants, so we've never even looked into it. I just learned on one of the threads here that most of the restaurants will allow kids in the earlier hours.
I contemplated a booking at Chops for our upcoming cruise, but at $30 pp I could not justify it. Different if it were just DH and myself.
We cruise for family time, so until the kids are older and the extra fee makes sense - its the MDR for us.
To be honest, I've always found something I like in the MDR. Yes, I've had the odd entrée that was not to my taste, but the waitstaff have always bought me a replacement.
Haven't been on NCL though.