SMT for passanger
"Can anybody convince me one way or the other? "
I have LOVED every second I've ridden my SMT. It is an absolutely perfect road bike.
However, I don't think it's much good for 2 up riding. I'll take my wife for an occasional squirt or a short trip to breakfast but I wouldn't consider going much beyond a tank or 2 of gas, and in those cases I'm staying off the highway so she doesn't get bored and start to realize that her ass hurts.
On the positive side the seat/footpeg relationship is good for my wife (5' 9" or so)
If your interest/concern is for 2 up I think there are better bikes.