In reply to:
Granted, there is a point of diminishing returns, where the tape actually starts to...pull apart
The failure mode isn't the tape pulling apart, but each pass over the heads scrapes a tiny amount of oxide off the tape.
What happens is you slowly, gradually, lose the high frequencies as the oxide wears away.
This exact situation nearly doomed the famous Fleetwood Mac Rumours album. The album production was so long, and involved so many dubbing passes that over the course of a year, ever so gradually the highs were lost.
They only noticed it by accident when playing a "safety" copy made months before. The highs on that tape were clear and crisp. This jeopardized six months of work.
The high frequency loss affected primarily specific tracks, e.g, cymbals. They recovered by taking the old safety copies with good high freq. tracks, and merging those with recent vocal tracks. This had to be done via a manual tape-to-tape sync, constantly adjusting tape speed by hand. It's a miracle it worked at all.
Needless to say many musicians with such experiences are happy with digital.
