With how much you drive your car, don't you want to put a quality product on it? There's no benefit to coilovers unless you plan to adjust the ride height. You can achieve your goals with higher quality components that will last for the life of your car (Koni shocks and OEM ZHP springs).
Just my $0.02.
'03 330i ZHP - Stock-ish
'02 330Ci - Megasquirted, E85'd and tuned by PFTuning.com