I love OKW, and it is my favorite place to be if I have a car, because you can park closer to your door, just like being in a condo.
You don't have to use a car there, the buses and the boat to Downtown Disney will get you around fine.
When I travel in large groups of 6 or more, we do like the minivan over the bus, as it is a nice way to travel without anyone not getting a seat on the Disney bus, and a place to leave our jackets and extra towels/change of clothing and other belongings, especially if we go to the water parks. It is very helpful in going to dine at OTHER Disney resorts. It is nice to be able to go out to get GOOD coffee off-site, or to grab snacks that are less inexpensive off property. If we do get the Minivan, we still send a couple of adults directly to the resort via Magic Express, as there is never enough room for like 7 people and all their luggage in the smaller less expensive Minivans.
But if you wished you could have a car for just like one or two days, use the Alamo or National Car Rental Care Center on property, and they will pick you up to get your car and drop you off after you return your car, they will even drop you off at a different on property location if say you want to go eat at a different Resort that day. We have done this for grocery shopping, dining out off property, and heading to the the International Drive area.