I've actually never heard the Mickey and Minnie thing, but I do know about the kiss goodnight. I had somehow missed it all but once in my many visits to Disney parks, too - we accidentally got to experience it in
Disneyland about ten years ago, and it remains one of my family's favorite memories.
For WDW, I made sure to catch it a couple weeks ago. I asked several cast members, and they had not a clue what I was talking about, but I trusted the DIS more than them - and lucky thing too!! At about 30 or 35 minutes after official park closing, the Castle goes through its color change (very beautiful) and then they make the special closing announcement with, I believe, Mickey and Minnie...maybe Jiminy Crickett? It's a very special thing, but I warn you...
MAKE SURE YOU'RE NEAR THE CASTLE COURTYARD!! We were on Main Street shopping so when it got close to time, I was standing in the middle of the street, assuming I could video tape it from there. Unfortunately, the announcement can only be heard near the Castle - I only caught the end of it, very faintly. Like I said, the CMs didn't have a clue what I was talking about when I asked, so I didn't know where to stand.
I hope this helps a little - there is video of it somewhere on the web, but I don't have the link. Hopefully another kind DIS soul will help you with that!!