Thinking some more on this, I guess my canon goes up to Amazing Spider-Man #150.
After the death of Gwen Stacy, we had the introduction of the Punisher, Harry Osborn becoming the Green Goblin and Peter getting closer with MJ.
Afterwards, the series spent some time spinning its wheels. The Len Wein run and first half of Wolfman run weren't really essential, to say nothing of the spinoff titles.
There were some good stretches, but it wasn't as consistently important. And some of the most important stories could be retold in major ways. For example, few would mind a cleaner version of the Hobgoblin saga, or an alien costume story where Eddie Brock is part of Peter's supporting cast.