A good AWD system is a huge performance improvement over FWD.
In the Audi's I've owned - it gives you so much confidence because it is so easy to drive fast without drama. I still have my 2001 S4 and it drives worlds better than my Mazda, just not as fast because it weighs over 3800lbs.
The '02 WRX I had (tuned to 232awhp) + coilovers would have ran all over my '08 MS3 in most conditions. The MS3 would have an edge in a roll-on highway race - but I hate that kind of bs and prefer to keep it at the track and autocross.
The drawback for me is, and the reason I was happy to jump in a FWD car again; AWD systems are HEAVY + AWD systems have more parasitic loss. I was intrigued by the MS3 because it is 3100lbs and has great handling and braking characteristics and most of all it has a pretty damn good power-to-weight ratio. All of that would change if you made it AWD. It would become a heavier car with less power to the wheels: handling, braking and acceleration would all suffer - and suddenly the MS3 is not such a bright star in my opinion. I would have gotten a different car.
Mazda should stick with what they are good at - good handling, efficient FWD cars, excellent small sports car the Miata, and for gods sake bring back a high-performance RXn with more power!
I considered the MS6 for a short time but reading about the "weird" AWD system turned me off. I have high expectations for AWD.