The auto shutoff is for reducing emissions as well as for economy. This article helps explain, in city driving with lots of stoplights it can improve your mileage:
https://www.edmunds.com/car-reviews/...save-fuel.html
As for the skirts on the Leaf, the owner must be a hypermiler; they like making modifications to their cars to get as much mileage as they can. It really isn't all that different than people who try to improve the performance of their cars...they have different end goals but both groups do things that may or may not help that much. The enjoyment is in trying things out to see what works.