I may be wrong, but I thought you could get all season tires and the square wheel setup on M sport. Or did you check with your CA and it's really not possible to combine those two options?
Assuming it's not, I think selling the summer tires and get all-seasons is a decent solution.
However, depending on how much snow Philly gets, I think getting a dedicated set of winter tires and wheels is a better solution like achopra said, and it probably wouldn't be that much more expensive. The reason I say that is if you buy the additional set of tires for winter, it means your first set is not getting used during that time and will last longer. The wheels are an additional cost, but 17" wheels can be quite cheap (look on tirerack). And with the higher profile tires, getting cheap wheels is less of a concern.
Your choice though, the all seasons should be fine unless you're driving on hilly snow/ice covered roads.