The Illusion of Change is probably the best approach for a serial like Amazing Spider‑Man. If it's applied correctly, it seems to most readers as if things are happening to their favorite heroes, and it allows the writers to put the characters into new situations. But if a reader looks carefully enough (which most won’t) they’ll discover that the elements they like about the characters are being preserved and most changes can either be undone or ignored by subsequent creative teams. It’s a method that has worked for decades, a compromise between a completely stable status quo, and characters growing old and dying/ retiring.
The origins of the Illusion of Change
Some cite the early Marvel comics as having established a consistent and permanent precedent for change within the Marvel books. They expect major developments to happen to the same characters in the current comics almost (or exactly) as often as they did in the Silver Age, where Reed and Sue got married and had a kid, Bruce Banner was exposed as the Hulk after maintaining a secret identity for years, etcetera. For Spider‑Man, this meant that Peter Parker was able to graduate high school, go to college, become friends with the guy who bullied him in his first appearance, become roommates and best friends with a spoiled rich kid, meet the love of his life, become a suspect in her father’s death and watch her get murdered by his best friend’s father, who died immediately afterwards paving the way for the best friend to become his next archenemy.
The problem with demanding that current comics to be like this was that during the Sixties, no one knew that the Marvel superhero comics, or the universe in which they existed would continue for generations. When Stan Lee wrote the silver age classics, he thought superhero books were a fad like sci‑fi comics, horror comics, western comics and romance comics, all of which were popular for a few years, and then disappeared.
As he explained in the book Comics Creators on Spider‑Man....
I was just happy that Spider‑Man has sold well enough for us to continue publishing it. Believe me, we never thought that any of the titles would last for as long as they have.When he realized that the success of Marvel comics was not just a fad, and the characters he cocreated might survive as long as Batman and Superman, Stan Lee and other Marvel figures determined a new editorial policy, now that they had to consider the long term fates of the characters, and the possibility that the appeal of the characters would be lost with further progressions. They realized that the continual “growth” of the characters would eventually lead to most either dying, retiring, or changing drastically from what made the characters popular in the first place. There really is no other option, save an eventual reboot of the Marvel Universe or somehow making the major characters immune to aging.
Ever since the first days of comics, the industry followed trends. There’d be the western trend and all of the publishers would rush to produce more Western titles. Romance books would suddenly become popular and all the westerns would be cancelled. A science fiction or animation trend would follow the romance books. There would be a new trend every year or two. When Fantastic Four started to sell, I just assumed that it was time for a superhero trend. I never thought that it would last more than two or three years, if that long.

Applications of the Illusion of Change
Marv Wolfman adhered to the Illusion of Change approach throughout his Amazing Spider‑Man run, which is why instead of killing off Aunt May, he wrote a story in which Peter Parker was told she had died, all part of an elaborate hoax. Peter Parker graduated college, but went on to a Graduate program, so they still got to tell essentially the same types of stories. Wolfman believed that the character should never be shown as finishing grad school. A milestone “To the Death” battle occurred between Spider‑Man and his uncle’s killer, a man who hadn’t been seen since Spider‑Man’s first appearance. The story thus seemed important, without causing any permanent damage to a recurring villain or supporting character. Peter was fired from the Daily Bugle, but got a job at the Daily Globe. Peter proposed to Mary Jane, but she said no. Peter and Mary Jane broke up, but there was always the possibility they could get back together, perhaps around the time he would get his job back at the Daily Bugle. Things happened, but not in a way that limited any future stories.
Spider‑Man joining the New Avengers was a perfect example of the illusion of change, given how easily he could be a solo superhero again. Peter Parker falling for a girl is another example, as writers can easily have the couple go their separate ways. That break‑up is another illustration of it, as the writers can easily have the couple reconcile.
With the illusion of change, the private subplots have significance, so the comics aren't just the adventures of a never-changing Spider-Archie. Characters remain accessible and consistent for new readers, and potential writers can hold on to story ideas for years before they get to use them, rather than worry about what will happen if the character and franchise becomes drastically different. For example, Mark Millar has some plans for future Spider‑Man stories somewhere down the line, which would probably become useless if Peter Parker retires being Spider‑Man and an Indian assassin takes over the identity to become the highest profile truly pacifist suphero.
The Illusion of Change and Spidey's Love Life
The greatest advantage of Spider‑Man being single is that it makes the illusion of change so much easier. With the marriage, Peter always has a loving beautiful wife to go home to, no matter what. If Peter were single, writers can shake up the status quo every few years without resorting to faking MJ's death, or sending her to California to reevaluate her priorities, which can easily have readers thinking less of the character, given what she's been through already, and how the marriage was presented as strong.
Meanwhile, all the things that happen to Peter and Mary Jane and fall under the umbrella of the illusion of change add up more obviously that if the things had just happened to Peter. In order to shake up the status quo, the writers may be tempted to make more permanent developments such as Peter Parker getting married and/ or becoming a father. These differ from break‑ups and new relationships, as neither can be easily reversed and both make the passage of time more perceptible. For all the talk about the constant growth in the Silver Age, the Peter Parker of Amazing Spider‑Man #100 was not noticeably older than the Peter Parker of Amazing Spider‑Man #50, and it was unclear how much time passed between those issues. Was it six months, two years or something else?
Some would argue that Peter being a bachelor is a static situation, just as much as the marriage. I disagree as “Peter Parker is single” encompasses several types of stories including "Peter has a girlfriend," "Peter has no girlfriend" and everything in between. "Peter dates Ursula" is a static situation. Until the relationship ends.
What Actual Changes Should the Writers Be Able to Do?

There are many stories you can do that won’t limit later Spider‑Man stories and thus represent the illusion of change. “Peter starts dating a girl” won’t limit future writers from breaking the two apart. “Peter has no girlfriend for a while” is an element of the status quo that can easily get changed. “Peter gets fired from the Daily Bugle” is a dramatic, but temporary change, as he could always get his job back. “Spider‑Man moves in with the Fantastic Four” is something that wouldn’t be expected to be a permanent part of the status quo. Writers are free to explore new stories with old characters, as long as it doesn't close other storytelling avenues.
A series like Powers, Saga or The Walking Dead should have developments for the protagonists and supporting characters which bring the story closer to a climax, as the stories are meant to come to an end, eventually. One mistake fans make when considering stories they'd like to see is that they'll often compare the series to a movie or book, something that's meant to come to a satisfying conclusion. In the case of a movie series, it's something that has one story every few years. It's not something that's meant to have a minimum of ten stories an year every year for the next twenty plus years. Meanwhile, Amazing Spider‑Man is essentially a never‑ending serial with a constant protagonist. It's a story that may just continue decades from now and that's something writers should be mindful of.