I'm planning on buying the Go Oahu card through Costco for when my fiance and I are staying at Aulani for our honeymoon in August. I've never used it on Oahu, but I have used it in Los Angeles and similar ones in Orlando and Philadelphia. For us, it makes sense since I'm a planner and I love having an itinerary and knowing what I'm doing each day. The way I figured it was, although it's a 4 day card, even if I used it only 3 days, it's still cheaper than the 3 day card on the Go Destinations website. AND since it has the Germaine's Luau feature added now (which is something we wanted to do anyway), it becomes more cost effective. That's just my two cents. It has a lot of "attractions" that we want to see, and having it "prepaid" with the Go Card makes it easier too. I'm not so worried with the not being able to spend time at the beach or the pool since we're there for a week and we'll have spent 5 days on Maui before coming to Aulani....and we're planning on going back in 2018 for my mom's 59 1/2 birthday.
All in all, I think it's worth it, but you have to decide if it's worth it for your family. HAVE A GREAT TIME!!