We're a family of 5 that typically drives from SW PA about twice a year. We generally stay in nicer hotels, and have a fairly generous budget (around 6-7k) per trip. We would much rather drive than fly at this point, especially with the kids and if it saves us money, then all the better. Even though we have the extra funds to fly, we don't see the need to spend the extra money just because we can. Flying is of no value to us, the extra time in Orlando not worth an extra 300 - 400+ hundred dollars (I have a spread sheet for our annual budget in excel; each vacation category is broken down) or the stress of flying.
I absolutely hate the hassles involved with flying. DH and I took a trip to London/ Greece in 2005. We nearly spent the entire thing in DC because of a missed flight. After being told numerous times to wait in the 4-6 hour United service line, I found a helpful gate employee (?) that was able to get us on the next flight. If not, the remaining flights were booked solid and we were told it would be 3-4 days before we could get a seat on a plane to London. Although we were able to get on the flight our luggage did not, and was subsequantly misplaced, end result we spent the first 3 days of our trip without most of our possessions. Coming home was smooth enough until our flight from DC to PIT was delayed from 11:00PM until morning at the earliest. We had enough, went to Enterprise rented a car and were home and in our bed by 3:00AM. It was a horrible experience and one I can not fathom dealing with kids in tow.
Again, each side has obvious benefits/ risks and each family has to be right for them.