Anytime you replace stock rubber with stiffer polyurethane there is going to be greater NVH transmitted to the driver and passenger, some owners may not notice or the bushings that were replaced were shot and not doing what they were supposed to do.
I DEFINETLY recommend getting the poly bushings for the sway bar. It helps get rid of the delorean brake shake, which happens under heavy braking. The bushing holds the front stabilizer bar rigid, which in turn helps keep the LCA from twisting backwards. In fact at the DMA spring social it was noticed that no many cars there was space inbetween the stabilizer bar and the frame mounted bushings. Toby at DPNW kit is great choice for this upgrade.
By the way my car has -eibach springs/marty mier's KYBs/front strut bar/boxed LCA/Poly LCA and Sway bar bushings. I can't speak for one modification by itself, but I can say that the car feels much more like a small, light, agile sports car. It almost feels like it pulls towards the inside of a curve, instead of the instant understeer that you get with the stock suspension set up. Heavy braking is a 100% improvement without the nervousness.