I suspect 2 separate problems.

I have a '97 850 wagon with 110K on it and had noises but pulsing in the
wheel when I made hard turns. After inspecting, I found slight leakage on
the rack, so I replaced and the problem was gone.

On your wheel shimmy, if you feel it in the steering wheel that's good
indicator it's in the front end. Who did your wheel balance? You might just
swap the tires front to back and see if the shimmy moves from being felt in
the wheel to being felt in the floor or your seat, then it was probably
still a wheel balance problem (eg out of balance, bent wheel, etc).

If that doesn't fix it, given your  attack by a wayward snow bank, I'd also
be suspicous about the front end and have a good front end man check it out.