I have the SMG and I completely love it. It makes the car for me.
Attitudes towards automatic gearboxes are very outdated in my opinion, and I am guilty of it too as I would not buy an auto Z4 – all the usual misguided arguments: old man's transmission, not in control, no skill, saps performance etc... but in reality they are far better suited to road cars than a manual. Unless you are wanting to blat around everywhere you go then surely the auto is a more refined driving proposition? I see the Z4 more of a tourer than a sportscar.
SMG puts you somewhere in the middle with the advantages of both setups. I do see the manual cars as being very outdated now I have lived with SMG for a while.