we wouldn't consider going without a car, but we stay for 2 weeks and like to visit shops and restaurants offsite as well as on.
Normally we will drive to all the parks but MK, (The TTC setup at MK means it's much easier to use the bus, elsewhere driving is very easy). we like to put dd into the stroller and then we just walk to the park - we have never been so far back in the parking lot that walking to the park was a problem - at Epcot and MGM by the time you have walked to the tram you are more than halfway there anyway, at AK it's a bit further but not an issue.
On the way back when we are tired, DH will usually push baby and stroller back to the car, while DD and I will use the tram - DH nearly always gets back first.
Anyway - I mentoin this, as the hardest part with the stroller is negotiating the tram, so we just don't bother.
We really like the car as we can keep stuff in the boot - cold drinks in a cooler, change of clothes, swimming gear etc, and we can get so much more done that we could possibly manage on the bus.
For example - we go to Epcot in the morning, after lunch we might decide to head out, hop in the car and go to Typhoon Lagoon for a few hours, maybe play some mini golf after TL, and head offsite for a pizza, or to Downtown Disney to shop, and then finish up at MGM to watch Fantasmic - there is no way you could do that on the bus - you would spend the entire time waiting for buses, trying to work out transfer schedules etc.
OK - I admit that's an extreme example and we would be exhausted at the end of that day - but the point is, you COULD do it, the flexibilty you get with the car is huge. Also, as soon as we get in the car, then the baby is in the carseat and she falls asleep - even if she only has a catnap and wakes up when we get to the next place, that sleep does her a world of good - she would never sleep on the bus, so that's a big advantage too.