I've also heard the lounge can be crowded with a wait, especially on weekends when people tend to start and end their vacations. Its also one time use, so you wouldn't be able to go back and forth from what I understand. You could also do a spa treatment on your last day, which would give you full access to their showers and facilities until you leave. We could have spent several hours lounging there! We thought the spa was worth every penny, and might be a nice option to head out relaxed from it before dealing with travel stress
We inquired about late check-out and they were not able to offer us a complimentary one, but they did offer us a late check-out of 3pm for $150. I don't know if this option is always available, but it might be worth inquiring about in your case because you'd need to leave for the airport not long after that anyhow. You'd have time for a late lunch/early dinner somewhere as well.
We didn't care much for the Swap Meet and it can also be very hot and sunny there. There's a new mall in Kapolei that wasn't open when we were there, and there's also Ala Moana Center near Waikiki which we loved. There's also the outlets in Kapolei and you could even grab some malasadas from the Leonard's truck there!
On our last day we had to leave for the airport earlier than you would, but we slept in a little and then packed everything up rather than doing it the night before. We then did the character breakfast which is a little more time consuming since it's so busy. We had about an hour to kill so we used the tablets and played the little Menehune game around the resort which was cute.