Only you can decide if it's worth it. If you dont want to have to worry about checking in at t-24 to get the best available boarding pass, buy it. I know a lot of folks will not buy it when leaving for WDW, but will for return so they dont have to try to check in at a resort desk, or cell phone, or guest service in a park, or hope someone back home does it for you.
Can also not be worth it if you have kids 4 or under, as they can board between A and B group etc etc..