It isn't an attempt to "boost" attendence at Grad Night, but to move Grad Night away from Magic Kingdom. If it moves, than MK doesn't have to close at 7pm, allowing more families to spend more time in the more popular park.
As far as the Halloween Hard Ticket, Disney needs something. Universal rules the month of October because of HHN. With the quality of that event (arguably) going down-hill, Disney has an opportunity to pull people away from it. Unfortunately, they need another franchise to capitalize on. Twilight Zone isn't enough (if they could even get the rights).
As much as I would love to see a Haunted Magic Kingdom (complete with Frontierland becoming a ghost town and Tomorrowland being invaded by aliens), MGM has the potential to directly compete with Uni.