After Hopperfan's advice we are going to try Bonnet Creek and see how it goes next year. I appreciate where you are coming from as my family really appreciate the 'onsite' appeal. However, we are 'monorail' resort only vacationers so that severely restricts our options and means a rather different budget!
Anyone an AP holder? That would save any parking costs at the parks. If not then just weigh up what you value more, a location that you feel offers better transportation, or more space and the ability to cook and wash etc.. As a family of 5, we really do need to use washing facilities for clothes and outfits, we go for 2 weeks usually so do not want to have to take that many clothes, so we will do 3-5 loads of washing per trip, having that in your building or even your room is such a god send! Means less bags, less air fees for additional bags etc... So that is also a saving from our perspective, often $150 round trip.
We did our first 'offsite' split stay as a family (i have done it a few times alone) and I can safely say that if you have a good location like Bonnet Creek, having a car is often a benefit! Using it to keep things in, ease of escape, and flexibility to get food and supplies etc... We loved our first week offsite and the freedom it gave us. The only better option from our experience is when staying at the Contemporary and being able to walk it, other than that it gave many of the same benefits as most hotels. I have 2 disabled children so we use disabled parking which puts you right by the TTC, which is basically the same as the walk from many of the long houses when staying at the Poly.
As Hopper says, there is no real comparison between a studio and a 2 bedroom 'suite'. But it will all depend on what your priorities are. If you truly want the vacation to be about not worrying about the car, parking, and other things, then onsite is the choice, but if you want some freedom, more space as well as comparable transportation options then bonnet creek would be the choice.
In reality, you can't go wrong with either, its just a case at looking what is the most important aspect of the trip. To my family, transportation is key, which is why we always stay at the Poly or Contemporary for a week or two. Others it isn't as important so its different for everyone.