@PrincipalTinker did a great job answering you but just to add my perspective, we thought the dining package was not good enough value and our family doesn’t like to ‘‘waste’’ time on longer meals when at Disney (we stick to quick service and snacks as much as possible).
While I wouldn’t necessarily call the dessert thing cheap or good value, it was perfect for us. First, it shouldn’t be called a ‘‘party’’…it’s a box !! But for us there was enough in the box for it to be our entire supper. So you get your box, you get awesome seats and you eat right there during the 30 minutes prior to the show (minimal waste of time). Compared to that, when we went to Fantasmic with Fastpasses, we had to get there a lot earlier and we had really crappy seats (although I think YMMV on this and you might get a better outcome than we had).
Also very important to us, we think a Fantasmic FP+ is a huge waste since you have to keep it all day and so you can’t get any additional day-of fastpasses. Our last trip, we add several additional day-of FP+ for both ToT and RnRC which we did multiple times on both days we were at HS.