Re this specific fork issue, I think it's fair to say that this sort of incident is exceedingly rare, and in my opinion not something to take into account for considering one bike vs another.
I agree it is rare, but I would put aluminum fork on my list of reasons to think twice about a bike that I planed to use for loaded touring or for high mileage. If I was comparing two equal touring bikes and one had an aluminum or carbon fork, I would take the steel one.
I have not intentionally avoided aluminum frame bikes, my folding bike has an aluminum frame (and steel fork). But as an engineer I have a bias towards steel.
I think you hear of more carbon failures than metal frame failures. I have specifically avoided carbon, have never owned a carbon bike or carbon fork. A friend of mine tours with a carbon fork, but that is his call.
In all fairness to aluminum, I have never heard anyone complain about a loaded touring bike that is aluminum that had a bad shimmy. I think steel is more likely to have a resonance problem than aluminum. There are advantages and disadvantages to all materials.