Surely whichever way you look at , thats a hardcore frame that you cannot trust? the rear triangle is so tight they are already a bit of a boneshaker, which is why I sold mine a long time ago and stick to steel..
If you got a bargain as a donor especially , no sentimental aspect then cut it up so no ones daft enough to retreive it from a skip and get hurt, as sure as the day is long however thats repaired it will crack again I think.
Even when gusseted etc, several friends had headtube cracks welded and gussetted, etc on downhill bikes, it transfers the stress elsewhere and the next bit cracks.. aluminum is pretty well known for this in all manufacturing.
Additionally theres cost of repair against buy a whole bike.. they are out there, as you have eluded too, patience will win the day.
Just my view obviously but ive worried about stuff like this then found a better one by the time its all done.. with multiple things in life, now I wait and let someone else have the hassle mostly.