FGD, your explanation highlights to me why if I am flying IFR by day to Warnervale (no IAP no forecast - need alternate), I can use Cessnock and its firm forecast as my alternate without it itself needing an alternate even though it does not have an IAP or navaid. THAT is when the LSALT +500 & 8km vis rule comes into play!
I don't know if your description of how come you were not holding an alternate in the first place for the original example would auger well in a court of law. Jepp ATC pg 304 3.2.12 b. couldn't be much clearer.