xluben posted about taking the factory WRX tranny mount, drilling a small hole, and filling the voids with, I think, silicone. Sort of a ghetto Group N. He said it did stiffen things up without adding too much NVH. Certainly cheaper and easier to try that first before hacking a Group N.
I went with a Torque Solution mount, Kartboy pitch stop, Whiteline cross-member bushings, Factory short shifter, Kartboy front and rear shifter bushings, and Anarchy Motive 1.5 pound shift knob. DEFINITE increase in NVH, but the way it shifts is worth it to me. Race Car.