If you want to talk your wife into a van, present the following scenario to her:
It's raining ... hard. You have to get the kids to school. Do you want your arse outside in the rain whilst buckling the little ankle biters into their seats or do you want it in the warm/dry van.
That's was the clincher whenever I wanted to get a conversion van for hauling the kids around years ago (back when they were still kids)