We did MNSSHP with my nieces and nephew on our last fall trip in 2015 and while I love it, it wasn't the best event for them. The kids were 8, 7, and 4 at the time and none of them made it to the end of the party. They were cranky waiting for the special character photo ops (even though this auntie did most of the waiting
), bored and cranky waiting for the parade and fireworks, they didn't like the spooky Haunted Mansion music playing through the park, and got upset tummies (along with a couple of adults) from the candy corn ice cream. More than half of our party ended up leaving after a few hours and were a little upset about having spent the money for an event they didn't really enjoy.
Personally, it's one of my favourite events and I have always enjoyed myself, but I don't think it's worth it for everyone. If your little ones are easily spooked or don't handle a late night well (or nap well like the kiddos I travel with), I would maybe re-evaluate the spending money and maybe do another special experience they may enjoy more at this point. This year, the kids have chosen to do the Pirate's League and BBB instead!
As a family, we will be skipping it on our October trip this year unfortunately for the same reasons. Down the road when they'll actually enjoy it and have a blast, maybe we will reconsider! I would take your family's habits and preferences into account in making your decision, and would also recommend having a time-management strategy if you do decide to do it so that you can get everything in you're hoping for! In any case, enjoy your trip!