I'm in your surrounding area and this is what I would recommend to you.
Get a set of replica 18" wheels (half the cost of OEM) from wheel dynamics or similar and mount Pirelli Winter Sports from the Tire Rack. Let the cheaper replica wheels take the winter abuse and save your more expensive summer wheels and tires for May to October use.
With a race jack and impact gun you can switch wheels in 15 minutes.
Some people will tell you put the winter wheels and tires on when you think it will snow but in the NorthEast a rainstorm can turn into a snowstorm within 5 minutes.
I think its better to run winter tires all season, And without snow tires the Boxster is dangerous in snow.
http://wheeldynamics.net/Wheels.html