If you do lots of table service within a year, it is worth it. We used ours first in June and made back the $50 cost after about three meals (three of us). Then we used it again in Aug and will use it again in Jan.
You either have to be a PAP/AP holder ($50) or FL resident ($75) to get the Disney Dining Experience card.
There are a few table service restaurants that will not accept the card, like Teppanyaki.