The Polynesian resort is my family's all-time favorite resort!
However, I think that the lower-cost deluxe resorts (Wilderness Lodge and the Animal Kingdom Lodge) are wonderful too! To me, the Polynesian resort has sentimental value, has some of the largest (non-suite) rooms on Disney property, and has our favorite restaurants, in addition to the best location on Disney property.
When we travel with our DSs who are now 18 and 16, it's like traveling with adults, not kids, so we need that extra space, and the extra bed, that the Polynesian gives us. So that fact alone gives me more value for the cost. (My DSs are big guys and the bunkbeds at the WL and AKL don't have much headroom, so those resorts don't have the best bedding configuration for us anymore).
My point in saying all this is that you should think about whether or not *you* will think it's worth the price difference or not. If the extra $100 a night will mean that you really have to tighten your budget, you might feel better at the WL, which really is a wonderful resort in it's own right. However, if the extra $100 a night really won't effect your budget at all, then I'd definitely say to go for it and stay at the Polynesian.
Have a wonderful trip, whichever resort you stay at!!!
