Even before we had kids we always loved the freedom a car gave us. Since we have had kids (now 4, 2, -1 month [#3 due in Sept]) we are even bigger car fans.
As for driving to anything other than one of the theme parks, a car will save you a ton of time and be much more confortable/convenient. That includes other resorts, DTD, water parks, etc.
As for the theme parks..............
Driving to the Studios and AK is very easy and rather convenient. We always drive to those parks. The parking lots are not that big and it is very easy to walk to the gates as opposed to taking the tram. If there happens to be a tram waiting when we park we may jump on, otherwise we walk. As for all the loading and unloading, I find it easier to load the kids/strollers/stuff into my own car, on my own time, in the morning as opposed to waiting for a bus and then trying to load it all on the bus when it gets there. Now here is where the car is really key - at the end of the day. If you happened to take the bus there is a good chance you may find yourself, tired, lugging the kids/strollers/stuff/whatever you may have purchased in the park out of the park. If it is late the kids may very well be asleep. Try getting all that stuff and sleeping kids on a very crowded bus, then keeping it all safe and contained for the ride, only to have to get it all off the bus again when you get to the resort. Now that can't be much fun. Now if you have a car you simply roll the strollers, sleeping kids and all, out to the car. A quick transfer from stroller to car seat leaves them comfortable and/or asleep. You pack everything up, no rush mind you, and head back to your resort. Once you get there you can get the stuff out of the car at your own pace, keeping the kids asleep if they happen to have gone off to slumber land, and easily back to your room.
Driving to the MK and Epcot can be a little different. The parking lots there are much larger and further from the gates. It isn't all that convenient, or even possible, to park and walk, so you may be forced to use the trams, monorails, or boats. For these parks the bus transportation might be a good option. Now, I would never tell anyone else to circumvent any parking rules for the sake of convenience, but I have seen people suggest valet parking a car at a resort that is convenient to one of these parks. By doing so you wouldn't be subject to any time limitations (usually 3 hrs) that resorts have on parking and you could leave yor car there and go to the parks. I still don't know if that represents a parking infraction, but it has been done, and condoned by the CM's at these resorts who park the cars. Unfortunately, such convenience would cost you $6 a day as valet parking is no longer free. Truth be told, we have had a meal at a MK or Epcot resort without valet parking and then popped into the park for an hour or two, but anytime we did so we obeyed the limit on any parking pass we may have received.
There you have my rambling thoughts on cars and the theme parks................hope it is of some help.