I agree with this, while im no suspension expert, my car currently has rebuilt standard GTR shocks with some funky green Japanese springs in them (the color coding looks the same as project mu stuff) which are reasonably stiff, but not too bad. The car however at stock height handled like shit, body rolling all over the place and didnt feel very stable.
Ended up getting a whiteline handling kit (front and rear swaybars, castor bushes etc) and I was amazed at the improvement it made. The car still has a bit of roll in it, but feels *ALOT* more stable when driving hard, and would be comparable to lowering the car/hardening the springs to improve handling.
Im now an advocate of doing things properly rather than just slamming a car on stiff springs to improve the handling... its a whole package, it was explained to me the suspension is there to do one thing, cushion the bumps in the road. The sway bars and other bits and pieces are there to provide the handling aspect to the car.