The Rubber Mats are a must if you live where I live - everyone one tracks in the stuff and it gets everywhere.  I got them with the car, in the spring I put the others in.  The other item I got you might think is over kill, is the rubber floor cover in the trunk.  It has a lip all the way around.  It is perfect for the winter.  Finally, the other overthetop item is the leather cover for the back seat - reason - I can throw anything in the back seat and nothing but the cover is getting wet or dirty.  Yeah it is a hassle, but when spring comes around and you clean out the car and prepare it for summer, it is like you have a new car.
http://www.bavauto.com/  - When the car came, the rest of the stuff was aquired then, I was stupid.  This site gives you all the same stuff for less.
As far as actaully driving a 330ci with snow tires - never have because my friend finds no use in them.  However, that being said, had I purchased a 330ci instead, I would put snow tires on it, no quesition for our winters.  I have zero problem with anyone wanting to put snow tires on a 330ci that live North, no question it would help.
However it is a Dream driving the 330xi in snow, it is like driving my 4wd SUV and it is even better because I have never ever had a car that works so well in the winter - with or without snow tire and/or chains.  
The 330xi is a cool machine when it snows and it is a Dream to drive - snowblow the driveway and get out and drive.  You can go up hills, down hills, stop, speed up, etc.  It is cool.  You are not getting stuck (well if I am stupid enough to run into a foot of snow - I am toast - agreed - pure and simple the main difference from a SUV and the 330xi.
Sorry, getting to excited, winter is coming.
 ![Wave    [wave] [wave]](/images/smilies/icon_smile_wave.gif)