Canceling the ESP to get cash back for mods was my original plan. Until they told me the refunded money would simply be credited to what i owe on the car, and not into my pocket.
So, if you got this baby paid off, I'd say go for it.
Did you roll the ESP into your financing and that's why it gets credited back to your payoff principal? The day I took delivery of my stang I financed the car and then paid cash for the ESP, I would think I would get the refund in this scenario.