When I started going to WDW, my oldest was a toddler. We stayed with relatives in Longwood, but the drive just kept getting worse and worse, so I started staying at hotels on "the strip" but the drive just kept getting worse and worse, so finally ended up staying onsite.
20 odd years later, I still won't stay offsite UNLESS there is a reason to be someplace else, such as a meeting, or a plan to spend most of our time at the "other" theme parks.
I agree that the luxury of taking just one bus/boat/monorail ride to your resort, in air-conditioning, beats taking a tram to your car, getting into a hot car, and driving back to a resort to take a nap/swim is worth the extra money. So is the luxury of not having to drive home after an exhausting day of walking around the park. (Although I have been enough times that this is no longer a problem; I only feel as if I have to see anything new, as I've seen everything else dozens of times.)
The fact that I can enjoy a glass of wine, or two, in the evening without worrying about driving is just icing on the cake.