First time we did MNSHSP we loved it! Not too crowded, loved the parade and fireworks. Next year we went and it was totally different-due to a huge (and I mean huge!) thunderstorm that forced Disney to cancel most extras (first parade, stage show, etc) Also the fireworks were delayed and even though they did eventually go off, there was no announcement they just started about 45 min. late. We were not in a good spot to watch most of them so that was a disapointment.
Also, since it was raining (sometimes pouring) off and on all night, all of the candy got wet. They provided some umbrellas for the CM handning out candy but the candy was completely out in the open. At one point we even saw them removing the Cards costumes from the CM along the Candy Trail so they wouldn't get any wetter. Also, I guess due to the rain, there weren't many costumed characters out. We only saw the Queen of Hearts along the one trail and she was in a huge hurry and didn't even stop.
When we got back to our room our candy was inedible. Too wet, and everything was sticky!

Also, I noticed a change in the type of candy that year vs. previous year. More generic candy, less name brand.
The main complaint I had with Disney (and I love Disney) was that we couldn't get any info from them. They made no announcements. The CMs didn't know what was going on (we waited to take a picture with Cinderella's carriage for almost an hour and they never re-opened it). All in all it was a huge disappointment and even though I would go again (on a non-rainy day) I'll never get my DM to return.
The night was so bad that they offered guest a free return ticket for one day at MK within the next year. We actually got a full refund instead. That's how bad it was.
That being said, as long as the weather is good (and it usually is at night) I would do it again. The fireworks are really cool and the parade is great! Collecting the candy is fun though you can get a lot of candy at the store for the price of the tickets.
I do recommend that you enter the park at 4 p.m. and make an ADR for about 4:15-4:30. By the time you are done eating you will still have time to do some rides before the party officially starts at 7 p.m. Don't waste a ticket that day going to one of the major parks. We have done a water park on
MNSSHP day, and that has worked out well.
I haven't done the one at DCA so I can't compare, but since DLR does a lot of Halloweentime stuff inc. in regular admission, I don't see myself paying extra to collect candy. I know there are other things (different characters, entertainment, etc.) but it's not enough to get me to fork over the extra $$.
Oh, and one last thing, if you don't attend and want to see the Grim Grinning Ghost Spooktacular (the fireworks) you get a great view (and some of the music) from the beach at Poly.

Especially awesome is the view near the end of the show when the fireworks go off all around the park-amazing! Last year we managed to watch the show twice from outside the park. Once form the TTC and once from Poly. Really cool, and free!
