If you feel 'compelled' to go see the monuments at Pearl.....then I understand that few days on HNL might be appropriate.
If you feel like you've always wanted to see Waikiki--and hear Hawaii 5-0 music in the background--then I understand why a 'few' days in HNL might be appropriate. Otherwise....I'd skip Oahu. Palm trees, cement swimming pools and movie stars. Ooops that's Beverly Hills. More like Palm trees, concrete malls and traffic. Lots of traffic.
Now of course, Aulani is nice and far from the city life of HNL, but you would be driving 30 mins to join that traffic every time you wanted to go see something in HNL.
The big island is nice, we're going next year I think, but it's also got a lot of driving because it's such a huge island. A short stay on Hilo would involve a large percentage of your time in the car to see the parks and volcano. Plus, it's not a lush jungle with white sandy beaches sort of island than many envision. We're going for the once in a lifetime trip to see an active volcano (and more), but will stay in the park for a night or two. I'm not knocking Hilo, but I'm saying that's it a different experience that's best appreciated over a week with relaxed expectations--not frantic sightseeing motives.
Kauai is the real 'pearl' of the Pacific for me. Crumbling, green volcanoes in the mist. White sandy beaches with few people. Dense jungle and grasslands. Water everywhere. Trails along cliffs that have NO ROADS. A grand canyon that isn't 120 degrees in the shade. Volcanoes, jungle, desert, sandy beaches. Check. The people on Kauai are real. (Not that they aren't on other islands). Real groceries, restaurants, farmers markets and more. If you love shopping malls, fancy stores, a plethora of amazing expensive restaurants and shops; don't expect to find them on Kauai, there aren't many. If you love cooking fresh Kauai shrimp on the barbie, cool mai tai's while watching the sunset and hiking to see waterfalls.... then Kauai is for you. The island is small enough to drive, but not big city traffic.
Maui is a bit of Kauai with a lot more development and surface area. Volcano, check. Jungle, dessert, quiet beaches, check. Good restaurants, check. Big resorts, check. So, you can drive to the ends of the earth, climb your volcano, hike thru the jungles to waterfalls, walk along sandy (busy) beaches and sit at a bar with music and people to watch the sunset.....or hike down to a black/red beach with few people, lots of water and amazing views. Of course, it's a 3 hour drive back to civilization.
If you can't do two weeks, my normal advice is one island. Too much driving, flying, changing to enjoy the experience.
If you can do 7-14 days, and feel the need to see Pearl and Waikiki, then I'd advise a week on Maui or Kauai and a few days on HNL to see what you've come to see and remember from TV and movies. So, 7 on Maui or Kauai and 3 on HNL. Might as well stay in Honolulu if you're going for the sights, it's a big drive to Aulani and back (several times) and you'll need a rental car.
Also, don't forget: the first day is a pretty big day of travel, even for West coasters. Early at airport, check-in, flight, luggage, rental car, drive, groceries, check-in, whew. Long day. Plan for it. If you plan to do HNL and see the memorials, you need to make reservations and buy tickets etc... It's NOT like going to a National Park as you normally would, there are plans to be made. Study it, you'll probably buy a tour. It costs $$$ and takes a whole day pretty much.
WM in Kihei is nice....the reviews are good for BI Worldmark. I'm pretty certain you could do better by Interval or RCI exchange though.
Good luck!