Aulani is in Ko Olina, which is a luxe golf community very close to Kapolei. Without bad traffic it is about a 40 minute drive.
If one has never been to Hawaii ( or never been to Oahu), and only has a couple of days pre or post cruise, as much as I love Aulani I have to agree. Iolani Palace is on Oahu as is the Bishop Museum and WWII Valor in the Pacific Nat'l Monument/Pearl Harbor as well. I found Pearl Harbor easy to drive to from Aulani IF not driving in rush hour. And that's a big if!
I would not rent a car for an entire stay in Waikiki/Honolulu as parking is VERY pricey in Honolulu. The exception would be if you plan on driving a circle island tour (I like the Gypsy app for this).