Why you SHOULDN'T go to Wacken -- or at least not this year
Sure, there are a whole bunch of reasons why you might want to go. However, there are also reasons why you might not want to go, and it's disingenuous to encourage people to go without mentioning them.
The first reason is that there's risks involved with any trip that involves as many transit changes as this one, and it's quite possible that despite the advice given here, you may miss a connection and find yourself lost in Germany. I've been lost in foreign countries where I didn't speak the language, and it can be pretty intimidating; it's tough enough just being somewhere where you don't speak the language, let alone when you don't know quite where you are. Add to that the risk of luggage getting lost, and it's clear that you have to be mentally tough and resilient enough to soldier on and get through in the case that something goes wrong.
Additionally, with this kind of financial commitment, you can't really just decide not to go if it's going to be a torrential downpour. My first Wacken was in 2005, the worst rain that the festival has ever seen, and while it was an awesome time, I got progressively colder and more miserable as everything in my gear got waterlogged. I planned smarter after that, but I did end up chucking out almost all of my camping gear because it had become unusable. Like on any other camping trip, the weather can get you down if you're not prepared for the foul-weather camping experience.
Also, this year Wacken is going to be changing. In 2006, the festival drew about 65,000 people and was more or less wall-to-wall people; there were additionally changes in the way that the camping/parking fee was handled that torqued off a lot of people. For 2007, the organizers are trying to work out the kinks in the Full:Metal:Bag system that caused the controversy, and they're also making radical changes to the infield layout, moving the Party Stage to accommodate more people. The campground will probably have to be expanded as well, but there's been little news on what the effect of this will be.
With that said, a lot of this stuff is kind of to be expected from a festival, and if the lineup is enough to make you want to incur the airfare expenses, you should consider this stuff in your plans, but not change them because of it. Pack a crash bag, put a box of trashbags in your main pack, and be decided to have a good time even hungry, cold, wet, exhausted, and drunk.