I just finished a 5-night award stay for that same base room/suite, and got a huge surprise upgrade at check-in to the King Deluxe Overwater Villa. And I'm only HH Gold (the check-in agent had mistakenly called me "Diamond" initially, but I corrected them and my paperwork did say Gold). So honestly, YMMV.

I have no idea how I got this "five category upgrade," but if I had to think of theory, I wonder if it was good timing. First week of September is probably the start of shoulder season, and I arrived on the Tuesday, after [US and Canadian] Labor Day around 4 pm. We were the only ones on our arrival shuttle, and I wonder if that gave housekeeping more time to turnover rooms from guests that left on the weekend. We stayed at the Hilton Tahiti a few days beforehand, and it was noticeably busier on the Sunday vs. the Monday and Tuesday. It wasn't as obvious at the Conrad, but I sensed more arrivals/departures on Fri/Sat/Sun.

You can see my posts earlier in the thread inquiring about upgrades. Ultimately, I did not email anyone prior to arrival about upgrades (just the concierge for dinner and spa reservations). One week prior to arrival, I got the automated cash upgrade offer emails from Hilton, but they didn't make sense for me. Especially, after I saw that the app already initially upgraded me to the Endless Lagoon View Pool villa. In terms of it if worth an OWB, it was my first experience in one, and and it was really neat, for free. Not sure at what cash rate I would have taken it. A few of OWB downsides versus the Endless View Pool villa I had initially expected to get: I didn't get a private plunge pool (maybe if I were diamond and really lucky, I woulda gotten a OWB w/ pool); there's less privacy cz the villas will be closer together (but wasn't a huge deal); and the OWB is all one big room (+ bathroom and closet) and don't have any separation. Whereas the resorts on the Motu Piti Aau (St. Regis, Four Seasons, etc.) all have their OWB facing inward in the lagoon towards the main island, the Conrad's face outward towards the open ocean (although you're technically still the lagoon). Plus Conrad's location on the tip of To'opua Islet makes it a windier area, and the water has a stronger current. On one hand, there's more reef around the Conrad to explore and you can do it right off your deck, but you'll have to be more cautious and assess the weather. It's up to your personal preferences, the main situations that would make me avoid an OWB would be the lack living/bedroom separation (e.g. you have a 3rd person staying) or especially if you have young children (kids under 12 must be accompanied in the OWB areas).