I agree, if a child is already in full-blown meltdown mode, then the best option is really to find one of the quiet spaces (yes, there are some) at the park and wait until he/she has regained some control. The key is in trying to prevent the meltdown from occurring. Suggestions include bringing whatever the child uses at home as a comfort object, noise-cancelling headphones can be a great help, a hand-held electronic game or other object/toy that can be used as distraction, frequent breaks with some favorite snacks (you can bring them with you to save $$), and I strongly recommend a stroller-as-wheelchair tag to provide the child with a "safety-zone" and buffer from the stimulation - a stroller with a canopy is even better because it creates more of a hide-away. You might want to plan to arrive at rope-drop, do what you can in the morning, and head back to the resort (whichever resort, we have never stayed deluxe) for a rest/swim/change-of-scenery in the afternoon. Then you may want to return to the park for the evening (unless the kids have early bedtimes). Speaking of which - I know it's vacation but we have always found that trying to stick to "normal" daily schedule (get up, meal times, bedtimes) goes a long way towards preventing overstimulation and meltdown.
Good luck and enjoy your vacation.