I thought I would add my 2 cents worth in since I also have a 07 EB expy. I think you will be happy with the gas mileage with what the expy offers. The 07 is by far the best that Ford has offered. I was happy with my 98 and my 05 but the 07 is really hands down the best made.
I live on the east coast with no hills, mtns, all flat land. I am not an aggressive driver. I average between 21.5 and 21.9 mpg. I think this is great considering what this machine offers in comfort and safety. I think you will love it and believe me, your wife will be safe inside of it.
Mike