Hmmmm. I wouldn't plan my entire day at MK around it, but I wouldn't miss it either.
As I understand it, the goodnight kiss is repeated every half hour or so, beginning at a half hour to an hour before closing. The castle begins to "sparkle", and the music to "When You Wish Upon a Star" starts. As the castle changes colors, a recording talks briefly about Walt's vision for the park, Disney's hope that you had a magical experience, and wish that you have a safe journey home.
For me, its the symbolism that means so much. My family attended an e-ride night toward the end of our trip. We stayed until the park closed, and by the time we arrived at the castle, the area was quite deserted. My family and I sat down in front of the castle along with a half dozen or so others. A beautiful starlit night, surrounded by my loved ones, all content from a wonderful vacation. It sounds a bit hokey, maybe, but the goodnight kiss was a wonderful sendoff for me.
And, just the fact they do it, tells me they're sincere. It kinda reminds me of the old Red Skelton show when, at the end, he would look into the camera and tell you, "Good night, and God bless". You felt like he was talking to you, and only you.
So, I won't plan my day around it, but I'll be there for it, nonetheless.