Thanks for your opinion.
I was sitting in my friend's E90 fitted with Bilstein PSS9 last week and I was surprise that the ride comfort is as good, if not better, than my std suspension even the car is fitted with 18" wheels and lowered (goods great). handling is 100% better than my std E90.
I sat on another 330i Coupe fitted with KW Varient 2 coil-over kit and again the ride comfort and handling feels much much better even the car is lowered...
Later I was told that our std suspension is tuned to be used with run flat tyres and hence the ride quality changes once we start using normal tyres. Not sure whether this is true...