The food is terrific! So, ya, I think it's worth extra cost. Ask the wait staff which night is "Italian night" in the dining room and book for that night, as imho that's the weakest night for the menu in the main DR.
Totally agree with Kuki! Italian night is the best night to book the specialty restaurant.
We ate in the specialty restaurant on the Legend and it was by far our favorite 'specialty restaurant' experience. It is amazing and IMHO worth every penny of the $30.00. Just make sure you go VERY HUNGRY!