I too live in the DC metro area and have not had too much trouble with rear wheel drive cars: '89 780 Volvo Turbo and '94 E320 MB. I learned on rear whhel drive cars in Chicago 40 years ago. Extra weight in the trunk is important, and it is better ahead of the rear axle than behind it. You want the weight between the front and rear wheels to keep the polar moment of inertia low, thus the rear won't "step out" in turns as easily as if the weight was at the rear of the trunk. The extra weight in the rear is used to get the car moving. Don't think about using this extra weight to get through turns faster. Every input from the driver, i.e. throttle, steering, breaking, must be made smoothly and this requires more attention and anticipation than on dry roads. A 400 or 500 series MB certainly has great torque, but any car will spin it's tires on snow. I'd say buy it for all the nice days, be careful on the bad days, and stay home on the few terrible days.
regards,
Mark