You are correct on all your points about the car repair professionals, awareness and so on. I have started my car repair career ~30 years ago with fixing carburetors and ignition distributors. Often I got caught in this fashion computer stuff and hook-up the diagnostic computer before doing a visual inspection just to figure out that a connector is loose or fuse is burn. All of this doesnt change the fact that to properly diagnose or repair an infinitely complicated modern [BMW] car you need OEM tool. In OP's case, if there are any kind of Vanos or Valvetronic code you have no means to do any kind of testing or adaptation without OEM. Having it is not guarantee for anything, but it is a fighting chance.