I kinda thought this topic was about sewing for a minute..
Paper Mario 4 should be more RPG and less platformer. Don't get me wrong, SPM is great and was a good experiment, but let's get the series back to what works for it: being a goofy fun RPG, with platforming elements in it (and references to past Mario games [not just the PM games, all of Mario]).
As for final bosses: the story for the last two PM games was fairly similar..
You think that Grodus was going to be the final boss, but he was just a pawn in Beldam's plan to revive the Shadow Queen.
You think that Count Bleck was going to be the final boss, but he was just a pawn in Dimentio's plan to revive the Chaos Heart (that was right, wasn't it? I haven't played SPM in a while..
I hope with the story for the fourth game, they take a departure from the Bowser possesing and try something a little bit new. I know that Bowser hasn't been possesed in all the Mario RPG's, but it's time to try a different take on the story..