Well the Z8 does not come in 3 flavors ranging in price difference of over $30k, so I don't think its the right comparison. In my opinion putting an ///M badge on Z8 is degrading its value as it more expensive than any ///M.

So, its OK for a 3.0 or 4.4 X5 owner to put a 4.6 or 4.8 kit but its not OK for a 4.6 or 4.8 owner to put an ///M badge.

Personally, I don't care what somebody does with their car as long as it makes them happy. Its their car anyway.