One thing to keep in mind is that winter wheels will likely see much worse road surface conditions than your regular summer set. I'm not sure about Seattle, but here in the NYC suburbs the roads are absolutely pathetic, especially in the winter. Light snow and slush tend to hide big potholes, some of which can eat lesser-quality cast alloy wheels. That might be why for the longest time ugly, black STEEL wheels were recommended for winter duty.
They're strong and heavy, so they help dig down to the pavement and they resist most damage.
You're clearly not going to put steel winter wheels on your M3, so maybe consider the strategy that I've used for my car--use your OEM wheels as your winters (there are plenty of 19" winter tire options), and then treat yourself to that sweet set of aftermarket summer wheels that you've always wanted. That way your car looks good regardless of the season, and you have a strong, high-quality wheel on the car at all times.
