I did the rubber washer mod yesterday. I put one 1/16" thick rubber washer on each side of the mount on each stud/bolt, 10 total. Total cost was $5, and it was definitely worth it. The rearview mirror doesn't shake noticeably anymore, and I'm not getting excessive resonance on cold starts. Noise is still increased slightly over stock, but it's not intrusive at all.
On a side note, I just want to be clear that none of my comments were ever intended to be a dig on TTR or their product. The mounts do exactly what they're supposed to do, which is safely keep the engine and transmission as stationary as possible. The guys who are pushing their cars to the limit need something more rigid than the casual DD modder, so I'm just providing my input on making the car perfect for the rest of us.