Yup, DVC guy here who rents a car every time now.
It's nice that if you don't want to rent a car, don't feel like driving, or can't for whatever reason, that WDW's transportation is incredibly effective. Just not as effective as driving.
My wife and I used WDW transportation a couple times, and it was certainly doable. The biggest drawback for me was the Magical Express back to the airport - they make you get there ridiculously early.
You can also use both together to make things easier - especially in the Epcot & MK monorail situation. Park where you plan on being last, and take the monorail to the other park. It might save time (especially with MK's annoying parking / transport hub situation), but at the very least it doesn't cost you any time, and you get the very nice Epcot monorail ride out of the deal.