I am going for third time this year, and I agree it is a must see. You will be blown away by the quality of the mares. The mare show used to be it's own event, but now is incorporated into a three or four day horse show. You will have the chance to see some super young horses under saddle too. Stateman was the Three year old Champion stallion at Rastede in 2008. He is just one example of the quality of horses that come.
I have flown into Bremen and or Hamburg. Bremen is closer to Rastede. I usually stay right in Vechta so I can visit some of my favorite breeders in the area. This year we are staying one night in Rastede, but I did not make the hotel arrangements, so I am not sure of the specifics? If you like more info. please PM me.
Joanne, if you can do it, don't miss it!!! I agree with Nancy in that the mare quality will give you a whole new appreciation for the importance of the mare line in the breeding equation. It's a great experience on all levels. I stayed at the Villa Linda in Vechta the last time and it was very convenient. I did rent a car, though, as I too wanted to visit some of the breeding farms - and don't forget the famous Shockmuehle tack shop. That's a neat experience in itself.