We attended the Luau - but it was in the back lawn. It was indeed pricey - $210 per person. The food was really good - better much quality and selection than Paradise Cove, but the show wasn't as good and viewing the stage was next to impossible. Had we known more about it in advance, we probably would have saved our money.
Unfortunately I can't really speak to the beach party, as we made the mistake of returning to the room to wait for the fireworks. After hanging out poolside all day and sitting through the 3-hour luau, my entire family crashed within minutes of sitting down on the bed. But, I definitely heard the fireworks. Based on the frequency of the booms, my wife and I figured it must have been quite the show.