Monkey Island 2 often feels like it's about the past. Almost as though Big Whoop allows you to return to your own past, although clearly in a dangerous way. These games have never tried to hide the fourth wall - even when it's just Guybrush quipping "Never pay more than $20 for a computer game." So, to me, it's often as though Guybrush knows that he's being controlled by someone who is simply playing a game.
Then you have a mind-bending ending. One interesting thing is that the Big Whoop elevator can take you to the alley on Melee Island - Guybrush's past, and for the majority of first time players, the place where you first encounter LeChuck. It's intriguing, then, that LeChuck can't follow you here - which of course makes it the easiest (and safest) place to construct the voodoo doll. After that, things get weirder, and you're catapulted further into the past - childhood. And maybe it's implied that LeChuck - somehow - has come back with you. Elaine has the final, tantalising word.
So if it's related to the world of dreams (and I do agree that the dancing skeleton scene is fascinating) then maybe it's all just about interpretation. You can take the game, the themes, the story in as literal or abstract a manner as you like, but the truth is never really tangible.