We typically fly when we go to WDW, but one year we drove. The distance for us (me, DH, and two boys) is an 18 hour drive, but it took a little over 20 hours with pit stops, traffic, etc. While theoretically it seems great to do it all in one day, I wouldn't recommend it. It's exhausting, especially on the way home. We never could have driven it all in one shot after doing Disney.
We did the drive over two days both down and back. We packed a huge cooler with as many snacks, drinks, and sandwiches as we could, and I'm not going to lie...it was nice to have a minivan to just load up. When we fly, we always have to be strategic about what we pack. When we drove, we could (and did) bring everything AND the kitchen sink.
We had a great family playlist of music that we could all enjoy on the way, and we played a hardcore license plate game. Driving from the midwest we saw over half of the 50 states in license plates! We tried to make the drive as fun as possible with movies, games, etc, but at times the drive was tedious and boring. That's just what you sign on for with a long car trip.
We are headed back to WDW in June, and in trying to figure out how to save as much money as possible, DH and I talked at length about the merits of driving again. Our oldest is now 15 and has his driver's permit, and he needs driving experience before turning 16, so it was attractive to consider with three drivers in stead of two. However, we crunched the realistic numbers and opted to fly. We guesstimated how many gallons of gas we used on our trip, added up the food we spent on the road (because even with a huge cooler, we still spent money on food on the way home), added up the cost of the hotel on the way down and on the way back, and decided that while flying is still more expensive, it's not hugely more expensive...it's only a few hundred dollars more.
The biggest thing that I caution you to factor in may sound silly...the Disney depression on the way home. It's a real thing, especially when you drive. You have a long time to think about how awesome the vacation was and how sad you are that you are reentering real life when you get home. The trip TO WDW was fun and exciting because we had the anticipation of being there to look forward to. We all were pretty crabby, and tired, and Disney depressed on the way home. Needless to say, the trip home was NOT pretty.
Whatever you decide, I wish for you a magical trip filled with lots of pixie dust and many amazing family memories! Travel safely!!