While I haven’t been to Aulani yet, I have been to Hawaii multiple times. Going to a Luau is quintessential Hawaii, and IMO if you haven’t done one it’s like going to Paris and not seeing the Eiffel Tower. Is it expensive? Absolutely, but they all are, you are getting dinner and a show. I have paid that much just for a Broadway show without dinner. Also, I would be shocked if you have dietary restrictions if Disney wouldn’t make accommodations for you. DW has several food allergies and again while we have never done a Luau DL, WDW,
DCL have all gone above and beyond and made her food she can have, I would be shocked if they don’t do the same. We are going to book it when we go in February and DW cannot eat Dairy, Gluten or Egg, so that wipes out most of the menu, but again we aren’t concerned about it and will of course report back after our upcoming experience.
If you don’t have a car and don’t want to explore other options I think you should book it once, do you need to do it every time? Nope, but much like the Grand Canyon, IMO you have to do it once.