The discount varies as does the timing, hence there being so many people in this thread waiting for it! lol
We chose the AP's simply based on cost of tickets to the parks, while we knew of 'some' of the other perks, i.e. discount for rooms, food etc.. We are also Florida Residents so get that discount on rooms too when it comes out, so we didn't really factor this in. For us, the ability to pay the tickets off over 12 months was also a no brainer! Takes a big chunk out of the up front costs. Now, if I had to pay out upfront and I had the money would i still do it? Probably, but if its financially a stretch to do it then i would personally prefer to do it the old fashioned way and eat the potential discounts in favor of less money upfront. However, in our case the savings were huge!
The availability of rooms and hotels will vary as will the discount, contemporary is always a fan favorite so it may be tough to get in. This is why I would book there at rack rate and then potentially add the discount as soon as it comes out. Shopping around can get you good incentives and discounts, i think mine worked out to around 22% from Rack rate without any AP or resident discounts, getting another 3%+ would be nice but won't make or break our vacation. Good luck!