Sleep masks for everyone! That sounds cool.
On the island with Morgan on it (Shell Island or something), Helmeppo keeps all citizens paralyzed with fear. Are you gonna let him off with it? NO! Join Luffy, Koby and Zoro to free the island from the iron grip of Axe-Arm Morgan, or assist the Marines to capture the Straw-hat once and for all!
I figured that another fun house would be fitting, especially with a Enies Lobby theme! Get to the Gates of Justice as quickly as you can, but be careful, as you must go through the Judicary Tower, where the Straw Hats battle to save Nico Robin from CP9's clutches. And you'll meet iron-hard wolfs, leg-cutting giraffes, bubblewomen, rushing fatsos, weird octo-rape-hair guys, bull-haired bartenders, elephant-sword wielding leaders and a lethal, murderous leopardman.
What would a theme park be without the water-ride? The stream leading to the Grand Line is extra ferocious today, and if you crash (not that you can), you're toast. But, don't rejoice because you got into the Grand Line, as you will be swallowed by a giant whale, meet two assasins and suffer a lame running gag.
Ever ridden a dinosaur? You'll have the chance on Little Garden, where you board a random dinosaur and watch the longest duel in history take place. Oh, and watch out for wax, paint, bombs and weight-changing lasses.
Give the bartender on the island from movie 4 two 100 beli coins, and qualify yourself for the greatest race in history: the Dead End Race! Get to the goal first to obtain 300,000,000 beli (or as I call it, either extra Beli (max 2,000) or 20 dollars)
I'm kinda out of ideas. I'll just read some manga and watch some anime to get some ideas…