Springs are only half the suspension. Coilovers also have the damper. If ride height is adjusted camber will need to be set again. The main bonus for coilovers is the ability to adjust the stiffness of the suspension, easily adjust the camber with adjustable top mounts and choose what ride height you want rather than being governed by a spring which once it's on that's it. First set up will probably be a pain and consist of plenty of trial and error until you get set up how you want. I recently bought a set of hks coilovers for £350. Bargain really considering the new cost of a decent brand.