Weve always had a car when visiting WDW. We have driven down and we have flown and rented. In the past, the cost of renting was negligible when compared to ground transportation between MCO and WDW. Now, with WDW providing free transportation with ME, its a little different. We will rent a car on our next visit, but we will be going places outside of WDW.
I agree with what MikeJ just posted. We can eat offsite on occasion and easily visit the grocery store and/or Wal-Mart. We LOVE using a car for the majority of our transportation. Its so nice to be able to get into our air-conditioned car when leaving a park where not only do we all have a seat, we have seats near each other. We have a cooler with drinks and snacks and can go directly to our next destination.
As long as we could get a good deal on a rental car, we would rent even if staying at WDW only. WDW maps and signage are excellent and driving around is easy and relaxing. I dont know how much of a factor the cost of a rental car is for you or how long you will be staying at WDW. Many people are happy without a car, but I know we wouldnt be.