I guess it all depends if you are taking a "Disney" vacation or a "Florida" (or California) vacation.
Up until about 10 years ago we took the "Disney" vacation and spent the week visiting Disney Parks, restaurants, shows etc and used Disney transportation.
Then we decided to rent a car and venture outside the Disney bubble and have never looked back.
Our vacations have switched to the "Florida" type vacation now and a rental car is a necessity for this.
Sure we still visit Disney, usually from 1-4 days. Spend a day or 2 at Universal, Seaworld, Busch Gardens. Spend a couple of days at the beach, take in some local attractions/festivals, venture out on an airboat into the Everglades, explore South Beach, visit the Keys or take a cruise.
Which vacation "type" is your preference?