DH and I honeymooned in Hawaii, including Aulani, this past September. My trip report is in my signature.
We stayed 16 days - spent 3 nights in Waikiki, 3 nights on Maui, 3 nights on Kauai, and 6 nights at Aulani. Might be too much for some but we were happy with it, and I wouldn't have changed it. We got a taste of the other two islands and now we have an idea of what we like and don't like. We loved Kauai but found it very humid and much less touristy/commercialized. Maui was a good balance of natural beauty and commercialization, but it was cooler and very windy. In September, we also found the ocean to be very rough and you really needed to be a strong swimmer. The exception to that, however, is at Aulani since they have the lagoon. That was perfect. We also found it to not be too crowded at Aulani - never had chair issues, etc.