It depends on how a 'gimmick' is introduced. I think, in the 80s, a lot of changes were made that could be seen, in hindsight, to have been 'gimmicks'. Examples include Spider-Man's black costume, Jim Rhodes being Iron Man, Magneto attempting to reform, Steve Rogers being replaced as Captain America, the Grey Hulk and so on. However, most of these were sold with total conviction, often by writers on a creative roll at the time, and good stories were told as a result of at least some of these changes that wouldn't have been possible had the status quo been maintained. Also, in at least one case, Spidey's new costume, they got around the creepy alien side of things and had their cake and ate it too by having the Black Cat give Spider-Man three cloth costumes that looked just like the symbiote, but were just regular cloth, so that, in theory, had McFarlane not made such a deal of wanting to revert Spidey to the red and blues, he could have remained in this look from there on in and it would (presumably) have become accepted by now, in much the same way as nobody clamours to revert Daredevil to his yellow costume.
Whether it's a result of the increased age of today's comic consumers, or due to the ongoing cycle of resurrected characters, restored status quo and so on, people are generally more cynical now, readers and creators both, and none of these wild changes, which still can inspire a good story arc (I quite enjoyed Superior Spider-Man, having expected I'd hate it), ever feel like they could stick.