First of all, the Skyline is a sports car, not a luxury limousine. Therefore it should have a relatively firm ride quality.
The springs are there to support the weight of the car, and the shock absorbers are there to control the action of the springs. (Without shock absorbers, the car will just wallow all over the place, like a Yank Tank).
My experience has been that dead shocks will induce a severe harshness into the ride quality. To get what you want, I would suggest something like a KYB replacement shock absorber, with a set of Kings standard height springs. While this will firm up the ride a bit, it will not give the harshness that dead shocks can induce (and I'm guessing this is what you have atm).