Definitely bushings, trailing arm, compensator and compliance especially, I had mugen version of those bushings on my gsr and it was a night and day difference from the stock mush. After that some good tires and driving events, like lots of them .

My experience with poly bushings is similar to vbspec. My car (240sx) was skittish and nervous at the limits with the ES kit, especially under heavy braking and in quick transitions. I talked with some of the guys on the nissan road race forums and swapped everything out for a mix of nismo(hard rubber), back to stock and a few sphericals(rear shock uprights and front tension rods) and the car's limits became VERY approachable, a quiet humming from the tires followed by a very slow slipping and slightly howling tires that was easy to gather back in. The alignment was essentially the same, I just added a little more caster since I had the adjustable tension rods.