I know this will come out wrong but.. Its a car. A depreciating asset. The factory winter tests these cars in the artic circle. They have snow in Germany. People drive porsches to the ski resorts (even those with snow!)
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If the car has been sitting a while, I would first worry that the battery isn't dead. Depending on how I stored it, I would consider changing the oil first, just as a precaution. On the other hand, since it is a fine engineered car and you've read your owners manual, you likely could just go out, turn the key, let it warm up and go for a drive
If you drive you Boxster on summer tires in colder weather, be prepared for reduced grip levels. So, instead of pulling .9g on the skid pad, it might only pull .8g on the skid pad. Don't hit any ice, don't expect any traction on snow either. Be smart and prudent. Enjoy your car