Personally, I love vans. I too have noticed that you can get a newer can for a lot more money. We rented a 12 passenger Ford van a few weeks ago. We got a solid 16 on the interstate at 70 mph. I think the limiting factor is the trailer weight it's rated for. I think the 5.4 is 7-8k lbs.. The V10 model gets to 10k lbs.
Honestly, I think those numbers are low because of a few reasons. Most people who have a van will load it up with people and gear and then try to tow a trailer. But that is just me speculating.
I love vans and would own one in a heartbeat. You taxes and registration may be cheaper as well in a van.
Thanks