In the past before the California Grill had their check-in on the 2nd floor anyone could take the elevator up to there and just watch Wishes. However I guess it got very crowded with a lot of guests doing that which is why you now check-in on the 2nd floor and are taken up in a special elevator to the restaurant. So this way they only have guests who had dinner there earlier in the evening that are allowed to come back and watch Wishes.
Anyway you can still watch Wishes from the 4th floor observation deck which is open to anyone, so you don't need to be eating a restaurant in the Contemporary to do that.