I think golf cart really depends on how you "do" Disney. For the adult trip it is worth it to us to have them, 6-8 people some of us coming back mid day to walk dogs, later nights....it just works.
For the trip with the kids we also plan to have one, but again its more about time savings then getting around. We could easily do the bus, but there are days in our schedule that I will need to go back and walk the pups, so having a quick way to do that without waiting for the internal buses will be a time savings.