Regarding dining plan or not, you'll hear different answers from different people. Some will say there isn't enough food in the lounge to feed you throughout the day. On the other hand, we've known people who only eat from the lounge when they are staying club level. Since it sounds like you're doing a split stay, you might just stick with the dining plan for the other part of your trip, and no dining plan on the AKL day. Or, if you plan on being in the parks, and not hanging out at AKL, dining plan could be good option.

There are so many variables which affect my advice, but whatever you think you'll want to do is the best choice.

Also, you have access to the lounge until the end of the day you check out, so even though you won't have a room, you can still use your card to access the lounge and extend your club level enjoyment