Never heard of anything extra. I believe just they are just busier nights so they can charge a premium. Personally I would avoid them. We prefer to go as early in the hol as possible and midweek, always been walk on rides for us.
We just booked are tickets, we had to go for 31st! and pay maximum ticket prices, but we don't arrive until the 28th and so was only on available to us.
We don't mind paying it as we were given $250 American Express gift cards from a company DH did some work for!
So it was a treat.
We just booked our tickets on Friday and although they are not for a premium date they were still a little pricey at $159.75 BUT they way I looked at it is .. we saved this much by booking our Ultimate tickets so long ago. We can use the savings on the MNSSHP which we've never done before so it's a new experience for us and we are very much looking forward to our trip his year
It's possibly a once in a life time event for us we know it would be a long time before we can go again at this time of year due to DS's school commitments he starts year 5 this September