We have been going to Disney for about 13 years now, 2, 3 or 4 trips per year.
We have rented a car for 1 day during all those years to go over to NASA, The Disney Transportation system is operated very well, Like anything though once in awhile you may have just missed a bus and have to wait 15 - 20 minutes. While your waiting observe some of the beutiful landscapes Disney has created or just relax. (you'll need it) We are a family of 4, DS 9 and DD 7