Just got around to changing the Intake Cam Position Sensor.

My preliminary evaluation is that this has fixed the problem. I won't know for sure for a few days of driving it to make sure it wasn't just a fluke that it starts up nicely now, but I'm pretty confident that the problem has been solved!

And I would like to thank andrewwynn for the advice :-D Saved me so much headache and hassle! The Check Engine codes do not indicate any issues with the Cam Position Sensor, as it hadn't completely failed. I think it was just misreading at low speeds and was in the process of failing. It's been acting this way for the 15,000 miles I've owned the car and god knows how long before I bought the car, so it could have carried on without totally failing and triggering a code for god knows how long from now too.

For anyone looking for a Cam Position Sensor, I picked up one on eBay for $33 from the brand "OEM Germany Ab Elektronik"

It is made in Germany and I have found references online indicating that it is the same sensor that OEM BMW sensors are, but without the BMW stamp on them. After closely inspecting it and comparing it to the BMW part I pulled from the vehicle, they are indistinguishable, every detail is identical, and it's not made in China junk from Amazon.

Thought I would update this thread with as much information as I could in case someone else comes along with the same issue ;-)