While buying a stiffer rear motor mount would help with some of the drivetrain sloppyness, it does not help with shortening shift throws like the TWM or our SSP is designed to do.
If you're looking for shorter shifts without hurting your wallet, a short shift plate is the way to go. We have a few local customers running our SSP with the TWM console shifter and noticed the greatest improvement once our SSP was installed. I have personally driven an 07 MS6 with a TWM shifter and our SSP installed; shifts were very short and precise, couldn't ask for anything more! A shift plate will also save you time on installation; our SSP takes about 10 minutes to install for even the most tool-unfriendly person due to the clear and concise instructions included.
Back to what the OP posted, if you're hearing a clunking sound when shifting gears, it would be a good idea to have the rear motor mount, as well as the other two motor mounted, checked for bad bushings. Since your car has low mileage, it should still be covered under warranty, but as we all know with these cars, we are at the mercy of the dealer regarding whether or not they want to do warranty work.
Hope this helps! Let me know if there are any further questions.