Not sure I agree that DCT is a must have from residual PoV. its just the usual dealership "no auto - no deal" BS. I think M3 buyers are not the typical BMW buyer in that plenty of them want manuals, as with everything its about who wants to buy what you've got.
I sold my old E46 M3 a significant premium to what the glass guide gave purely because it was Estoril Blue and had a Sunroof of which there were very few examples available. I had two chaps who wanted the car badly enough they coughed up alot more.
Neil J. ///McRae -- Alive and Kicking -- neil at DOMINO.ORG
M3 DCT Alpine White -- M5 DCT Monte Carlo Blue