I have not read every reply, this thread is just way to long already. But I see many flaws in your cost analysis. The big one being it's too generalized.
How much a plane ticket is going to cost depends on where you live. I, personally, can get cheap flights, but my sis, YIKES!! Where they live, there is no bargain. They don't live anywhere near a big airport and must drive 3 hours for a small airport.
Getting dropped off and picked up at the airport really isn't an option for us. It could happen, but not so easily. And it certainly wouldn't be free. So then you DO have to factor in the cost of parking and gas to and from the airport. And at our airport, chances of your car being broken into if left for a long time goes way, way up. And that opens up a whole 'nother can of worms.
Second, not everyone is a family of 4. We're a family of 5, and 6 by next year. Therefore, you have to add in the cost of TWO more plane tickets. And, I'm finding more and more that we are seeing bigger families v. the 2 kid families.
Your depericiation is off. That number includes gas & maintance along with lost value. And if you are talking resale/trade-in value, the amount you lose tapers off quite significantly at 5 years and also at 100K miles. So, if someone (like me, is going to keep their car ~10 years and will most likely put on close to 175K in that time, one trip here and there to Disney isn't going to matter). That will also depend on your vehicles specific make and model.
We have never paid $2.50/gallon, even when we went at the height of gas prices. We driving east not south from the east. That makes a huge difference. I paid under $2.00 for gas two days ago. Gas prices along our route to Disney are about the same, sometimes less, than what we have here. Also, when DH had the company car, gas cost us nothing, even for personal use. Same with no maintaince and depericiation. It was pure free transportation.
Your food cost made me laugh. We never spend anywhere near that amount on food for a larger family. Besides, one must eat no matter where they are at: home, hotel, car, plane. And your choices in the car are actually much more economical than in an airport or at Disney resorts. Which also puts into the picture, that you aren't held prisioner at Disney to eat if you have your own vehicle. You could go to the grocery store to stock up. Or out to an offsite restuarant. So, over all, your food costs are going down.
We drive straight through, so the motel cost can be cut out totally for us. Who ever isn't driving sleeps. When the driver becomes too tired to drive, switch.
I'm still trying to figure out what you mean by free time lost by driving. Time away from the vacation? Not in our case, driving days are added. Actually, if we flew, we'd either have to pay for a hotel room on Friday night (more than the cost of our gas both ways) or fly in on Saturday afternoon where we'd lose the whole morning that we normally have. We do the bulk of our driving at night (less people on the road, easier on the kids) so no time lost at all. We've actually figured out the only sleep loss is about 4 hours for me and DH actually tends to get more sleep than at home. Plus, we enjoy the drive. We get to see sights, bond as a family, use the time to do things that might normally not be done. My kids don't fight/bicker in the car the way I guess some siblings do. I don't know if it's because they sleep the bulk of the trip, we prepare better, have more space between them, or they just get along better.

It's just not something we deal a whole lot with.
The time you have flying does not factor in airport travel time. Airport security time (showing up early, getting through security). Time spent waiting for planes. The delays it seems we always have. Time getting the luggage. And time getting to the hotel, including time waiting for your transportation.
Then of course, if you fly, that would mean a rental car for some people, especially if staying offsite. That adds to the flying cost.
Flying also has a lot more hassles associated with it. Secuirty restrictions. Hauling car seats. Gate checking strollers. Lost luggage. Damaged items. Being limited to what you can bring (number of bags packed [DS#2 has health issues, so major issue for us], what souveners you can take home albeit by size or thing). Extra time packing. Unable to have freedom. With flying my kids are way--WAY--more irratable. Having everything unfamiliar. That alone makes me want to drive. Hurrican season can make you a prisioner. Lost money for changes in vacation plans on many of those "good deals".
We actually used to fly all the time and was forced into driving one time. We had such a great time driving, and saved so much money, that we decided to drive from there on out. And, yes, your risks of an accident go up the more you are on the road, but overall the other time throughout our vacation that we are not on the road, actually means in the week we go to Disney, we have lower risks because at home we spend more time in the car.