We finished our stay January 1st (7 nights) using points (360k points) and can pretty much confirm what is written here. I am Diamond and we did not get any upgrades (also did sign up for a NOR1 upgrade) but the hotel was also fully booked out. On points there was no option to get 2 beds so we added a roll away bed for our son and the charge is relative high with 75 USD per day.
The Tapa tower room was ok, I did check in online about 15 hours before we arrived because I saw higher level floor rooms disappearing. We got exactly the room I checked into (no upgrade at all) and asking at the reception did not make a difference. We did get late check out (12:30) on the 1st of January.
We also go the 20 USD per day Diamond benefit and used it at Starbucks and the Tropics bar. We did not use the (overpriced) breakfast buffet. We did have breakfast twice at Hatsuhana (not part of the hotel itself but in the little Village and you can with a bit of pain get the charge on your room) and liked it and was decent priced.
There is plenty of things to do in walking distance and we did like the location. We did not have a rental car and just rented 2 x on individual days using Hertz in the Hyatt (a bit of a walk) which worked out very well (I am Presidents Circle and was in and out very quick, making a reservation 2 days ahead of time was both times no issue with car availability) and saved parking fees. One day we did use a service that included snorkeling gear to go to Hanauma bay (was barely more expensive with the ride then just renting equipment alone) and other then this we also did use Uber or Lyft quite often (Chinatown, Pearl Harbor, Diamond Head).
We did not like the pools much at the complex (the large pool was closed twice for some unknown reason) and the beach was super crowded.
In general we felt we got a really good deal with the points during high season, the hotel is nothing special but also not bad (rooms relative large but no view from our standard relative low floor room at the Tapa tower) and for points we found it a good deal around Christmas and New Year (arrived December 25th and left January 1st). The complex is huge and very crowded but we didn't stay there enough to be bothered. It was more a good located base with a good enough room. As already written Diamond's get nothing special except the (small) credit.