Welcome to the Zoom-Zoom Team! I liked the 2010 Mazda3 2.0L loaner I got while my MS3's wheel bearing got replaced, though it really needed a stick (it had an autostick feature, though).
I agree 100% with JtspellS- upgrade the rear motor mount. It will take some slop out of the shifter, the steering will feel a little more direct, and wheel hop will be reduced. I use this one on my MS3 in 75-durometer flavor:
http://cp-e.com/content/mazda3-mazdaspeed3-engine-mount
The only vibrations I get from it (after breaking it in) are very faint and only when the A/C kicks in.
Use a synthetic gear oil like Red Line or Motorcraft XT-M5-QS to smooth out the shifting even more. The RMM + the Motorcraft gear oil has transformed my MS3's shifter from vague and mushy to smooth like buttah!
You may also want to look into grounding your throttle body. Supposedly it enhances the throttle-by-wire's response a little. You can cobble the grounding wire together from scrap or McParts store items:
http://www.flex-innovations.com/mz3_tb.htm
Sit down. Strap in. Shut up. Hold on.