For our trip last month, we considered flying. We have always driven, it's about 14 hours from where we are in Maryland. We considered flying instead because of the price of gas now but decided against it because then we would have needed to rent a car in Disney. We've never taken the WDW buses, we always use our van.
We also needed the van because of all the souvenirs we knew we'd be buying, & they did amount to $1500.00 - - no way was I going to pay to ship all that stuff home.
If saving the $400.00 is a big plus for you, then I'd drive. For me, I would use the money on extra souvenirs!!!
BTW...about the long trip in the car with the kids...I look at it this way...in the 1800's...if the pioneers could spend weeks on end, day after day, in a covered wagon with their kids (with no DVDs or Gameboys to entertain them), then surely I can spend 14 hours with my kids in the car.