Mario Golf and Mario Tennis for the N64 are some of my favorite games. Their sequels aren't as good to me, but they certainly aren't the worst things ever. Same goes for Mario Superstar Baseball and Mario Strikers Charged (which I applaud for being stylistically unique amongst the spinoffs and amongst Mario games in general).
"Brighton and Twila, the sun and the moon, have always hosted the party."
First of all, if Brighton is the sun, why is Mario helping him out? Didn't the sun, like, wanna kill him in SMB3?
The Mushroom Kingdom clearly has more than one sun. The one you're talking about is the Angry Sun, which was probably made by Bowser. Did you forget about the sun that guards Flower Fields in Paper Mario?
Second of all, no they haven't. Hudson apparently forgot about Toad, The Star Spirits, Millennium Star/Tumble, and the generic enemies.
The plot of the game is contained within the Book of Dreams and didn't actually happen. It even takes place in some sort of "Mario Party World". Same goes for the plot of Mario Party 2, which was just an animatronic stage show at Mario Land.
"I know, let's play Mario Party to solve their feud!"
How will that solve anything? What they need is some anger management or counseling. ANYTHING would've been better than playing a board game. Talk about extremely awkward.
They did the same thing to determine who would get the Millennium Star in Mario Party 3, plus if my theory above is any indication, it's just a fairy tale that didn't happen.
Really, I'd put the plot of MP6 above MP5's Story Mode, which felt worse than your average children' educational television program.