Shave sums it up well. You get the magazines, then the opportunity to attend events. The events usually include exclusive ride time before or after normal operating hours, and will often include meals, behind the scenes tours, Q&A sessions, auctions of parts and collectors items, and other things. The events are not free to attend- there is a cost to get in to them, but you can't attend most of them at all unless you are a member of ACE (or in some cases like Holiday World's Holiwood Nights event, another coaster club)