I presume with these ones that if you lower it you are compressing the spring, correct?
If so, the more you compress the spring the firmer/shitter your ride will become.
If you dont like them, and they are not damper adjustable then maybe its time to invest in some quality suspension, usually stay away from jap coilovers as they love to be stiff.
As for stiffness of ride of a R33 GTR, my car was as stiff as a gokart on standard suspension.