I just talked to a new ST owner yesterday that wanted to use the same 17" wheels in the summer and winter. The mounting and de-mounting of the tires each season will tear up the finish on the wheels and promote corrosion. When we had the Fiesta Movement ST, the only marks on the car were from the dealer replacing tires and then again when the winter tires were installed. The 17" wheels also filled up with snow and vibrated terribly. The 17" snow tires are also far more expensive. The steelies are cheaper, but tend to look horrible. My brother uses steelies on his Fiesta and the car looks like an abused rental. I prefer to spend a touch more and pick up a decent set of aluminum wheels. For us, we run winter tires longer than summer tires, so best to have a decent looking set. I install the winter set in late October and remove them in late April or May, depending on when it warms up. 15-20 years ago, I could install the winter set in December and be back on summers in March. Those days are over.
A little winter tire story for everyone:
A few years ago a friend of mine bought a beautiful Mercedes C class. He had always wanted one and finally got to a point in which he could afford it. The car was a few years old and came with a nice set of performance summer tires. I asked if he was going to get winter tires for it, and he didn't think it was needed. The first snow of the season, he lost control of the car going down a hill in the neighborhood and crashed his Merc into a pile of decorative boulders at the gated entrance to his neighborhood. The car was totaled due to all the underbody damage. No matter how good of a car you own, the only thing touching the ground is 4 patches of rubber. Don't ruin a good car by picking the wrong tire for the season.