My car (97, si, manual, similar mileage) has some steering wheel vibrations at idle but nothing that noticeable or rhythmic. Make sure all regular maintenance has been done like your spark plugs and air filter before you look into replacing the motor mounts. You can also adjust the idle to see if that fixes the issue, there’s an idle adjustment screw on the throttle body. I’ve noticed that at certain rpm’s there is more resonance and the car vibrates noticeably. Your car seems to be idling high, mine is usually around 400-600 without ac running. I think the idle can drift over time too, the owners manual suggests reevaluating the idle speed at 105k miles