One thing you can't buy is time. Whether you drive both ways or work in AutoTrain somehow, you're using up a significant piece of your vacation driving. It sounds like your trip is about a week...I wouldn't want to sacrifice that time driving. I'd fly it...
There is truth in what you wrote but given the state of flying comfort nowadays I'm happy to get on the train from time to time. It's great at allowing DGD time and space to do about 75% of her homework packet before our Disney arrival thus less long faces at the Disney portion of the trip.