the other week, i installed Eibach springs and Bilstein B6 dampers on my skinny. can vouch for the springs (3rd set in as many cars), but at this stage, i'd say 'no' to the Bilstein's. they seem way too hard, and the ride remains crashy.
i tried them for something different, but wouldn't do it again. my other cars have always had KONI Sport, which is what i'd recommend instead.
there's always heaps you can do to a car, and the 155 seems no different: springs/dampers, brake pads/discs, panel filter, full exhaust, chip, wheels/tyres, tint windows, machine polish the exterior, gearknob, handbrake handle, HID xenons, etc, etc.
EDIT: updated opinion on Bilstein B6: my Eibach-Bilstein combo has softened significantly after approx 600km+ to the point the comfort is very acceptable, and i can appreciate improved damping. still a little bit 'under-damped' for my liking, but this is subjective. i now DO recommend the combo if that's what you prefer, though if i did it again, i'd still buy KONI Sport instead.