My 128 didn't have sport seats, but my 135 does (power sport seats). As far as I'm concerned the sport seats are very much worth getting.
Just like the steering wheel, the seat is a part your body comes in contact with while driving and so you get feedback from it. And also like that beefy steering wheel, the sport seats adds to the driving experience.
That said, my 128's seats were very comfortable and I have no complaints, I just think these sport seats are superior. And I'm not sure I'd feel the same if my sport seats weren't power - not so much for me, but my passengers always seem to be adjusting the seat's position.