FINAL UPDATE:
It was the alignment that caused everything. It simply wasn't done correctly, and it was the SZL sensors that were out of wack, causing all the issues. BMW re-aligned the car for me, free of charge, and everything's been fine since. Unfortunately, during the alignment they discovered that my right front LCA tension arm is off slightly because they cannot get the caster aligned on that side, meaning I must have hit a gnarly pothole at some point. The good news is that it's baaarely out of spec, and I've been assured repeatedly that it will not cause excessive tire wear on that side. Something I will need to keep my eye on though.
Thanks for everyone's advice though, learned a lot about the car through all this haha.
And on a side note, I'm loving the Sumitomo HTR Z III's I got on there now in place of the Bridgestone Potenza RE050A's. Better handling, smoother ride, quieter, longer treadlife... can't go wrong
