Growing up, we drove from Humble, TX to Melbourne, FL to visit family at least every other year. As an adult, I've done it once since but only because we had a family reunion in Mississippi on the way.
Sounds like MapQuest is a little optimistic on the time. I-10 routinely has construction between Lake Charles and Lafayette. Plus there are bathroom, food, and gas stops. Even if able to combine those stops, it still takes time.
You should be able to fly direct on Southwest (Hobby) or Continental (Bush)for $200-$250 per person. Sometimes, it's less (I found Continental for $178 the other day). By the time you add up meals on the road, gas, and hotel if you stop overnight, it generally breaks even on cost between 4 - 5 people depend on your choices and gas mileage.
If you have 5 or more people, multiple drivers and the time to spend a very long day to 2 days driving each way then driving might be an option. For us, it would mean me driving the entire time. I rather spend a couple hours on a plane and get there. Plus, I'd hate to make that drive after my stay at WDW. Leaving the World is hard enough without facing a 2 day drive home

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The challenge with flying from Houston is that the first flights are 7-7:30am. That puts you at WDW around lunch and facing the debate of using a full day ticket to go the parks for half a day. To avoid that dilema, we try to fly the last flight out of Houston and stay off site that night or preceed our visit to WDW with a visit to my relatives in Cocoa Beach

. The last flights out are around 6 typically, sometime 8, so have to cut your last day short a bit too so you can get to MCO.