Agree with you totally gIzzE.
The way I drive the diesel suits me so much better. Like your mate (did) I tend to work in the 1~4k range, so a petrol is not getting a proper work out. With a diesel I use more of the potential of the car everytime that I drive it.
I would contest through that the 335d as a mainstream high emmisions vehicle will see something of a hit in the short term, but... they won't get quite the hit of the 335i with it's top end tax level (before ED). The M3 will hold it's residuals because there will always be ethusiasts that will want one and it's also in shorter supply.
Given a few more years the 335i/d will supplant the E30 M3 as the car that all the kids want and the old guys in the BMW car club are all driving.