I've worked at 3 restaurants that have done it, and they've won 3 separate events. None of them are worth it. You will lose valuable seating during your busiest times to people who are going to use the tickets and get waters. That means not only are you losing money for the food, you are losing money that you could have made from those tables.

As for the new guest acquisition, there are much, much better ways to do that. Pay Buns and Bites or Phantom Gourmet to come and review you, you'll get a much better bang for your buck.