A combo of Starlight and HEA might be a good seller, but they might do it separately unless the HEA party alone has not been selling well.
It will be interesting to see what viewing location of Starlight turns out to be more popular. I say this because depending if there is new parade route lighting effects in some way, they probably wont be the same through the whole route. MS and the hub will, as always, be the most popular. Town Square and Frontierland will be the weakest unless they have added new lighting to those area. Of course some people prefer the starting and end points of the parade.