Well, the dues are higher than most resorts unless you purchase a subsidized contract. No difference in taxes or anything like that as it's all rolled up in the dues.
Some people have reported closing taking longer with Aulani and I think I remember seeing something about having to notarize your documents because of Hawaii's rules (but I'm not 100% positive about that).
Just some food for thought, we used SAP to stay at Aulani and found availability to not be an issue currently. You may not get the exact room you want or dates, but there is availability. So in my opinion, I would buy there only if you truly want the 11 month booking window and exact room type/view.