No perks but there are activities only open to groups, i.e., safari dinner, Wishes fireworks cruise, Illuminations dinner. A large group of us gets together every couple of years. This year we had 30.
Let everyone make their own hotel reservations but tell them to be sure to give the magical gathering number (which you can get by calling the number on Disney's website). This way if a few of you are staying at the same resort, they will try to get your rooms close together. This way if people change their dates, it's not you that has to call to make the changes.
I agree about don't try to stay together as a group (just plan on breakfast or dinner). Cell phones are great to keep track of people.
Safari dinner was great - sorry we didn't do it again this time.
Wishes cruise this year was a disappointment. Last time there was a fantastic dessert bar before leaving. This year - prepackaged desserts (chips, pretzels, etc). Yuck!
Illuminations Dinner was good but didn't do it again this year. Dessert was served on one of the terraces but if they are doing the same desserts as on the Wishes cruise, it's not worth it. Last time they had great desserts too but don't know if they changed too.
All of the above are at an additional cost to you so it can get pricey.
Cyn