If your gripe is "too much roll," the solution is anti-roll bars. I would only look into coilovers if you have very specific transient, dynamic body motion things that you want to fix. Roll angle through a steady corner is a spring issue, and anti-roll bars will fix that without the can of worms that crappy coilovers opens.

If your gripe had been "I'm concerned about the degree of rear-end low-speed compression during part-throttle mid-corner dips," then we could talk about what coilovers might do to help you change that.

Also, keep in mind that all else being equal, lowering your ride height will INCREASE roll on the S2000.