I don't have a shopping cart, but if I was going to contact failed orders, I'd probably also throw in a discount to encourage them to come back. Seems pretty easy to track whether that works or not. It would work with me.
I abandon carts sometimes when I don't like shipping, or if I'm not quite ready to buy, or sometimes I throw stuff in carts even when I'm not serious. A discount in any of those cases could quite likely get me to buy.