Hi, Sara!
Whether or not to use your personal car is completely up to you. If you decide to drive to the theme parks, standard
parking is complimentary for Disney Resort Guests. If you use
Disney Transportation, buses will be available to you to get you where you need to be!
Personally, my family always has a car. We drive to most locations, with the exception being the
Magic Kingdom. The Magic Kingdom is so much easier to reach via bus since the buses drop you off at the main gates of the theme park, whereas if you drive, you will need to park at the Transportation and Ticket Center which involves trams, monorails, and a lot of added time.
If you plan to visit any resorts for dining, you will find driving yourself will be much more efficient than transferring buses. Just let the security guard at the resort's entrance know you have a dining reservation and they will direct you to visitor parking (have your dining confirmation number handy).
You can decide day by day, park by park. Your kids might enjoy the bus rides, mom may not feel like driving, or dad might be tired of waiting for the bus, so each day will be a new adventure whether you drive or hop on the bus.
I hope that you find at least one long afternoon to avoid ALL transportation and simply take a nap and relax by the pool. Remember to relax during your magical Walt Disney World vacation!
Cathy