I'm gonna chime in and say that it would be a nightmare to go back to stock on this thing ($$$$), unless you got every single little part you took out in marked ziplock bags. I can only imagine how annoying it would be to follow the sometimes vague ESS instructions backwards. BUT, there is no reason to take it off, you'll find your buyer.
To whoever is considering selling their Z4M because they're bored of it, this is the shot of live you need. A proven 11 second car.