Well, a personal decision, but 16k JPY is steep to me. Yes the size of the premium room is way better, but only makes a real difference if your party is over 2 pax or 2 pax with big suitcases as in the 2 Singles room it'll get tight.

The rooms overall are nothing fancy, older ANA CP style, clean and all but not luxurious. Location is the main thing the hotel has going for itself.

As to possible upgrades, even as Diamond I got nada and they deposited 1k points per night to my account for not providing an upgrade. As a Gold, you have to be lucky to get anything.