I did it once with my mom (active 80s) and my son and nephew (both early 20s). My nephew who really likes the characters loved it as there were lots of them out that aren't usually there. Character lines, though, are pretty long. He also lives in Orlando, so it's a little different than just doing a day at Disney. My mom, my son, and I while we all had a really good time together were more one and done on it. My son and I both prefer a regular day at the MK to the party. My mom I think is just kind of bored of the Magic Kingdom in general (the party was her idea instead of a regular MK day). She'll come to be with us, but these days prefers a different park as she has just been to the MK too many times. You can do way more at rope drop my son and I think than late at night here. The party was sold out and seemed awfully crowded (even the second parade) etc. The free cookies were meh. Ride lines weren't all that short. The only really short ride was the last ride we did on Space Mountain right before midnight. The gift shops on main street stayed open quite late into the night and it was kind of fun seeing all the adults who were really into Disney. We left the party at 1:30 a.m.
As for rides (anything we would have wanted to do during the day -- the headliner things) were all open and available.
If someone else was doing the planning and asked me to come along, sure. But if like most of our mini Orlando trips my son and I are planning it, we would not do it again.
The short answer is no, the party is not worth it to me. While the MK is always fun, in reality I was disappointed in the party -- I had a misconception that it wouldn't be as crowded as it was.