We just tried The Plaza for the first time on our recent trip. We were not on the
DDP this trip, but have been on other trips. It was the perfect meal for what we wanted: a simple sit down meal, not heavy, long, just casual. It was perfect for that!
The food was good. Not outstanding, not mediocre, just good. And sometimes good is what we want. The soups and sandwiches were a perfect meal. A lot of times we share meals at Disney because the portions are so large. I'm glad we didn't this time around because the portions were more "real world" restaurant sized portions.
For DDP: not a waste of a TS in my opinion, just not as "pricey" as some of the others. Sometimes you don't want a huge, complicated meal.
For OOP: honestly thought it was a little expensive. We had 5 people in our party, we got: 1 cup of soup, 4 burgers or sandwiches, one kids' meal, 2 iced teas and our cost with tip was $85. Thankfully, DD got ice cream with her kids' meal (the best value as you get soup, entree, dessert) as we all shared it

.
My only big complaint and tip is that we were (as I felt) "stuck" in the back room, like a little gazebo room. I felt like we were in a penalty box. Although we had a nice view of the castle, the room lacked the charm that the main dining room has. It was also cramped in there and DS and DD had to constantly scoot their chairs in for the servers to get by. Don't get seated in the penalty box!
So I say "Yay" IF you go in there knowing what to expect.