If it were me buying again I would hold out for comfort access, no doubt about it. Having the SmartTop takes away some of the disappointment, but not all. I can't tell you how many times I get in the Z4 & push the button like I do in my Nissan or my wife's Toyota and THEN remember to have to fish the key out of my pocket to start the car.
I often carry things in the trunk, so the CA-like luggage loading features of the SmartTop are key for me. But even that isn't as good as the trunk loading feature I had on my SL600; the top was out of the way in seconds.
Of course, everything else on that car was a decade behind the times, which is why I'm much happier with the Z4.