Well, I wouldn't call myself "savvy" but I know enough to be dangerous
My background is (sadly) not racing or HPDE type driving but I do have an engineering degree and briefly worked for an OEM supplier of brakes so I have a little "book larnin'" but not as much actual behind the wheel test experience as I'd like. As generally I need to select wheels/tires without having the opportunity to test them first, I tend to ask lots of questions and overthink things
The main thing that I remember about scrub radius is that if you had too much the vehicle would pull to the high-mu side when braking with the front wheels on different surfaces - that is the one thing that was really dramatically evident even to the "un-sensitive" - the difference between an average passenger car and a typical 4WD truck was astonishing in this respect. Now it's not a problem if you're ready for it and know how to handle it, but it seems that most people who drive vehicles where this is an issue would say "scrub what?" if you tried to explain it to them... But usually such vehicles have ABS now and it's tuned to mitigate that effect, but at the expense of ultimate stopping distance.
So caster/camber aren't easily adjustable on a BMW? I ASSumed caster wouldn't be but I also ASSumed that camber would be... but I haven't really been underneath the car much at all yet mostly because I need to buy myself a good low profile floor jack that will fit underneath it! Even my little cheap Chinese portable one won't fit under the side skirts :/ I just had a local shop give me an alignment after I swapped my winter wheels/tires on, and they were able to get everything within spec somehow.