my new limit
flying vs. driving is now about 425 miles. The worst problem driving out on the American Great Plains is actually boredom (if you don't count the road food). I advise you to consider the weather when planning your trips as winter in the area you are considering can take most of the fun out of driving.
Saying that, I now agree that driving is a more comfortable way to travel when you consider how much time you have to wait in airports, baggage claim, etc.
Learn what you can about American motel chains and pick one that will give you the most benefits, points, miles, free breakfasts, etc. and suits your style. I'm getting very fond of Holiday Inn Express motels and the newest of the 'suites' motels such as Homewood (if you are going to be in one for more than one night).
I can do 425 miles in a day before my mind is so numb I have to stop.