i see what you mean Kalikala, the appeal of TSI to me at the moment is the fact that it is quiet,and a place next to POTC in adventure land would be cool but i think that if it is called pirate island then it should be an island,to me it adds a small sense of realism to it.
i really like your idea of being able to dig for "treasure",but i think ellaborate that,make going to the island an adventure.
ok here's my idea.
the rafts could be rethemed to look like small pirate ships or make them bigger with a bigger guest carrying number say make it the same size as the boats that take you from the port orleans resort to DD.
once the raft/boat docks at pirate island there could be a CM stood there telling you old tales of piracy this is how we find out about the hidden stuff.
hidden all over the island could be things that have something to do with these stories,things like blackbeards hat and sword stood in the ground somewhere on the island or small pieces of the cursed aztec gold could be scattered all over the island and you have the task of finding how many there are,(obviously these would be embedded in stuff like sand, the pavement, rocks and other things and will not be able to be picked up),just little things like that for the kids to find and see.and then have something along the same lines as the boneyard at AK in donoland usa, but instead of bones it could be things like chests and gold.
on one side of the main island there could be the black pearl moored to the island and a small roped plankway from the middle desk and the beach.and it could be fully recreated (obviously it would be downscaled a bit so as to allow the liberty belle to pass by it).