You have a very nice car, and the least expensive fender-bender you might have will cost far more than a second set of winter wheels / tires.
You also chose the oversized 20" wheels, which (forgive me if this is insulting) are a 'vehicle' for sucking your wallet dry. The entire automotive industry is going to larger wheels because they look cool, but at the expense of crappy ride comfort and short tire life. It allows for huge brakes, to stop cars with unnecessarily large engines. Neither immense engines or brakes do much when stuck in traffic, which has become a fact of life in this former cow-town.
45-series rubber cannot handle on ice or in rutted snow anywhere as well as taller tires, no matter what kind of tires you have. The high profile tires do something yours do not; they flex.
I regularly preach to friends and strangers alike to MINUS-SIZE their wheels, not plus size them, especially if they are a second set dedicated to snow use. I have a close friend driving the ML-350 who dropped from 19 to 17 inch wheels, spends half as much now on tires and brakes, and loves the ride improvement.
Your ML-350 can run a 17" wheel. The tire size would be 235-65-17. A Michelin Xi2 in that size is less than half the cost of the 20" variant, last twice as long, and is far safer. The difference in tire price alone will pay for a second set of wheels in short order.
Chains are a horror. You will be soaked, cold and miserable by the time you get them on, if not killed first by errant traffic. Two years past a close friend teaching full-time at Vail made the conversion to snow tires, after two weeks reviewing what chains to buy and three days using them. (Digs in the Vail Valley are tres chere; his affordable winter rental was up a nasty steep driveway, impassible on his summer tires but easy on the Hakkas he finally bought). He had been on all-season tires all his life, and discovering winter tires made him born again at 65.
We're skiers; it's all about catching first chair. May the traction be with you.