There is discussion on this topic a little further down the board you might want to take a look at.
You'd just have to guesstimate which ones you'd eat at and how many times to see if you would have any savings.
I have run the numbers based on how many times a week we usually dine at the specialties and the cover charges for those and it does not appear that we would benefit from it, at least on a seven day cruise. We probably average $70 per person.
We usually end up in the MDRs and buffet several times, and probably only average 3 times or so in specialties during a cruise. Based on the restaurants we like, even going to Cagneys twice, we'd have to hit the specialties about 5 times in order to just break even and that's way more than our normal usage.
Personally, I just want to eat where I feel like eating and not have to worry about whether or not I'm getting my money's worth out of the UDP.