Here is some extra info from questions asked on M3 Forum (and answers from Phil at Vibra-Technics):
"How much is it for the replacement inserts for your motor mounts as well?
And what are the life expectancy of these mounts vs oem motor mounts?"
Its hard to tell life expectancy, we have not seen a failed mount yet in normal service. The only parts we have seen with damaged rubber are from crash damaged parts from the track. They were re-built with new inserts. The inserts are around $60 a car set.
"And is there a DIY on how to replace the rubber insert ?"
The only slight difficulty in rebuilding is holding the top cap. We use an assembly jig with a 3 jaw chuck to hold the top cap whilst you unscrew the centre bolt. The 4 m6 bolts holding the top mount ring in place are easy to remove but you nee to hold the body somehow.
"Are there any specific signs of failure that I should look for to know when to buy replacement inserts for the mounts?"
The only sign you would get if there were a failure of the rubber mount is a significant increase in noise because something would be touching inside the mount. It cannot pull apart in any case so its completely fail safe.
Also Interlagos08 stated that "just so everyone knows,
they are off for holidays, and will be back after the new year, however the discount period will end 1/13/13 providing the world wont end."
So it you may not be able to ask questions until then. If anything else pops up in the M3F topic, I'll let you guys know.
I also added some info to the OP.