We purchased our kids parkhoppers 2 week before our trip in Feb and was asked for dh's aaa card #. I know booking a trip online requires membership as well. Call and find out.
I don't believe they are any cheaper than any other advance purchase price. They do however include free parking at Mickey & friends lot which can save quite a bit if parking.
If you are staying at a hotel with the AAA discount, they might ask you for your card. Hmmm... I'm trying to remember the last time we went, and if they asked me for my card. I had all of my reservations and tickets already from them, so maybe they didn't. You might check on that.