Sometimes I think back to the times when I started reading Spidey (around 2012) and how much has changed since then.
I started with Big Time and then slowly made my way back, while also reading the current comics (Dying Wish) at that time.
What I can say is most of the important stories (Kraven's Last Hunt, Death of Gwen Stacy and Jean DeWolff, Origin of the Hobgoblin, etc) were already collected, so it made for easy reading.
But then there were stories that weren't collected. Stuff like Gang War (80s), the Tombstone stories in Spectacular, Web (I know a lot of the Web stuff is considered bad) of Spider-Man, and many of the 'Spider-Man' stories as well. I think a lot of the 'Spider-Man' material is still uncollected.
Most of the stories I ended up reading in single issues were eventually collected, which is nice to see.
There's still some stuff ("Name of the Rose", "FACADE", and other Web stories that I enjoyed despite being terrible) that haven't been collected, but I don't see it happening. Most agree that Web of Spider-Man was the weakest of the books at that time, so I don't see most of the material being reproduced in any form.