to save over $100 bucks for every hour of driving? Yeah, I'd drive. While it isn't WDW on the road, it is part of the time you are spending as a family. Also, flying isn't always trouble free...we once had a flight that had to stop in Atlanta (medical issue) from Chicago. Everyone absolutely understood the need, UNTIL it took 5 hours to get back in the air after the passenger was accomodated. Total it was almost 8 hours of being sidetracked. Every item used for medical reasons had to be replaced, checked off, luggage recounted (or so we were told) all I know, is by the time we landed at MCO...we had only saved 4 hours off of our drive time...and that trip we were also renting a car which added to the bill so we would have saved that. Now, we get to the airport a minimum of 2 hours early so we do tack more time onto flying than the average person probably, and we allow an hour by cab to get there/back, so right there is 3 hours that we would be on the road. We are about 19-20 hours each way if driving.
Now...all that said, we do stay on vacation for at least 8 non-travel days. The drive does take it out of us more than flying, and we are usually shot the day after arriving. We are pumped and hit the parks the day (or night) we get there, but then are toast the next day so usually hit the pool,grab groceries, enjoy one of our favorite character meals and unpack carefully so we are efficient the remainder of the trip because we are commando in the parks. I agree with others if you have 7 days or less, just eat the cost of flying if you can.
We wish we were just 4 hours closer..honestly, we would drive straight thru. We do that from Chicago to Colorado...takes us under 15 hours usually, leave at 2-3 a.m and arrive for dinner.

Either way, enjoy your trip, great ages for the kids to go!