I say take your wife to a couple of dealerships (if she'll go - my wife is very hesitant to set foot on a lot
). I showed my wife the xB and sat in the front, adjusted the seat and then got out and showed her how I fit in the back (there is definitely more room in the xB than the other cars you're considering). I had about 6.5 to 7 inches of space between my knee and the back of the driver's seat. I'm 6'1".
Then I sat in the Corolla. When my knee hit the bottom of the steering wheel (wheel was adjusted as far north as it would go), she saw that I didn't fit well and that space would be an issue and told me to forego the Corolla and it's 38 mpg, and go with the Scion, because it had more room.
Was I disappointed in the outcome? No way. I wanted the Scion and have been trying to convince her it was the vehicle for us... errr.. me. Since she'll have a larger vehicle for her and the kids and I need a good commuter car for work...