We've done the unlimited plan at both the Polynesian and GF. Both resorts also offered a less expensive plan that was more limited. Don't remember the details of those plans though. Our experiences were all a couple years ago.
Anyway, the unlimited plan was for up to 5 drivers. It was really unlimited but I know if it is a busy time some people reported having to check in after an hour to see if anyone was waiting for a boat. We never were out that long anyway except with the pontoon boats.
I remember reading that it was for 4 people at WL but have no first hand knowledge of that.
However, I don't know if those plans are even being offered anymore?

I know it wasn't during one of our Polynesian visits and I haven't seen any recent reports of the plans.
I should add that at the GF and Polynesian both, you had to be a guest of that resort to do the plan. I don't think that was true at the other resorts.