For a relatively short trip like that I would stay at one hotel, period. And I'm a hotel explorer at heart. I wouldn't move once and certainly not twice. You'll waste a lot of time changing hotels and very probably end up seeing less, not more. (Especially a pain if it's like checkout is 12 and checkin is 4 and you can't get into your room early.) Base yourself someplace, by all means rent a car, and drive to some of the other things you want to see.
If you're only staying at the Hilton Waikoloa for one day because it's a really cool looking place you'd like to see, I suggest doing exactly that - just see it. (I've stayed in my in-laws Waikoloa timeshare condo a couple times and done just that. IMO the Hilton is "a nice place to visit but I wouldn't want to live there." Just getting to your car will be a half hour excursion, never mind doing it with dive gear.) It's true if you're not staying there you can't use the cool looking pool and beach (though I think you can buy a day pass if you really want.) But IMO it's not as great in reality as it is in the pictures. But you can walk around, see the pool and grounds, see the dolphins, walk around and see all the nice artwork, and take the boat or the tram that goes around the place.
