Just just installed Formula Dynamics' springs on my '06 Coupe. Huge difference. Really, it's like a different car wrt the handling. It's not super-cheap (cost of the springs, installation, plus re-alignment), but very worth it.
I just purchased a set of Formula Dynamic springs and plan on installing them soon. How much did you lower the car - 1 1/2" or more? Did you lower it the same all around? Is the car much stiffer on straight highway? I drive with a set of Goodyear F1 GS D3 tires that came with the car. Do you have the details of the alignment - toe in, etc? It looks like there is no reason to change the shocks.