Yeah, all of those cameos were just for looks and aesthetics, really. Disney doesn't own their rights, they just made quick cameos (which also works as some nice advertising for those characters).
And man, if we do get Gravity Falls characters, which I hope we do, and a playset, I really want there to be three characters. Dipper and Mabel would be a given, but Grunkle Stan would be icing on the cake. After all, the theme song itself gives the three equal emphasis. And without spoiling it for those who haven't seen it, Season Two especially showcases more of Grunkle Stan.
Brass Knuckles for Melee combat and using a smoke bomb-like blinding projectile sounds really nifty.