I notice alot of people seem to recomend coilovers over just springs (and shocks if it was me) for a street car, ive had coilovers in street cars before and they are horible far to stiff for the road, unless you are changing the springs to suit the street i think coilovers are over kill, The only advantage i see in coilovers is you can custom tune your height ect, but that is really only needed if your going to the track.
Wouldnt a decent set of springs and shocks with dampner control be far more suited to a street car, as you can pick the correct spring rate and dont need to worry about cert.