I've only stayed onsite once, and that was at the POFQ when my son was 2.5 yrs old and we had a very good experience. The positives are that the resort seemed small enough that it was VERY easy to walk anywhere in it - the gift shop, the restaurant, the pool, laundry, the boats, the bus stop, etc. He really enjoyed the pool although he would not get in the big one - only the kiddie pool. At that age that is understandable. Your 4 yr old would probably go for the big pool however! We were there in early May and had very nice weather. I frankly don't remember the busses to and from the parks being a problem - I don't remember stopping at other resorts. However, we did end up just taking our car cause we couldn't see the advantage to taking the bus. The car was faster and the parking was free and we could haul our big stroller more easily. The only bus problem was getting back one night from Downtown Disney.
I've only stayed at the PO, as I said, and I was a bit surprised how small the rooms seemed compared to what I've paid, for example, the La Quinta on Intl .Drive in Orlando. However, the room is big enough to exist in - I guess that would be my biggest wish for that place is a bigger room!
Enjoy!
Carol G.