It's necessary to build up tension and show some things that would otherwise require contrived methods to show, I guess. If you just leave this chapter out of book four, and explain it all at the end, you'd have to be far more limited with the explanation and leave out some of the good things in this chapter: the social commentary, the Peter characterization, and the like. And you wouldn't have that nagging voice in your head telling you there's more to fear than just the Tri-Wizard Tournament tests. It's similar in the other cases. I think these chapters improve the books they're in and the series as a whole, honestly.

I don't know, it works great in terms of misleading the reader. We obviously think that the events at the World Cup will prove hugely significant once we figure out what happened - if a reader is particularly attentive and trying to figure out what Voldemort's up to, he must assume the plan has changed since the first chapter. In the meantime, ultimately far more important events like the Moody garbage bins incident are slipped in in far more subtle ways. But then in the end the World Cup proves important only for Hermione's house elves thing, and for the Bagman thing.

This book simply has more balls to juggle than PoA, so to speak, and Rowling does so quite competently, I think, throwing red herrings around along with real hints, and setting up or further developing tons of characters and plotlines for later books while keeping this book strong in its own right. Okay, Voldemort's original evil plan is of a remarkable simplicity, but so what? The book has enough complexity with everything else that it doesn't really matter.

Indeed.

I guess not, but I'm having fun in this reread with trying to put myself in the head of characters for whom Rowling does not spell everything out in detail - Snape last time, Peter now. And for Peter, it still has to grate.