This effect can happen a lot with online fanfiction as well; any particularly well-executed fanfic that takes source material in a new direction is likely to spawn a horde of imitators, rapidly turning the original author's new and innovative take on the source material into a tired cliche. With fanfics that are Long Runners or suffer from Schedule Slip a story can actually go from innovative to cliched before the author is even done writing it.
A lot of older fanfic suffers from this, especially in large, well-trafficked forums like Harry Potter, when a fic that invented or popularised a popular piece of fanon is examined in light of what went after.
Likewise, the old apas and zines seem quaint and silly in comparison to the internet. Many younger fanfic writers never heard of the days when it was incredible to get four or five novel-length fanfics circulated in a year.
This is a notable problem with many old Redwall fics, particularly The Urthblood Saga, that deals with the theme of "noble vermin". When these fics where written back in the late 90's/early 2000's, the concept of including good foxes, rats and weasels in a story based on a series that is so strictly black-and-white was fresh and challenging. Nowadays however, it's rare to find a fic that doesn't include it, or that plays the Always Chaotic Evil mantra from the official books straight.
A vast majority of Ranma ½ fanfics written after 1998 or so were built almost entirely upon Fanon established in earlier works by notable authors; the absolute worst case of this being the Flanderization of Akane into a brutally violent, abusive raging bitch with a hair trigger and no rationality whatsoever—which was given legitimacy in the very dark "The Bitter End", a story which painted a darker picture of the Ranmaverse and reconstructed this portrayal, with a Freudian Excuse, in the process. After TBE, "psychotic Akane" became one of the biggest cliches in Ranma fanfiction to the point that most people roll their eyes and groan when they see a story going in that direction.
Also, the amusing parody crossover Sailor Ranko spawned an entire subgenre of Ranma fanfiction.
Harry Potter has inspired one of the most prolific fanficcer communities ever. As a result, tons of clichés have formed over the years. A modern reader might find a fic way back from 2002, filled with clichés and not realize those he's reading the first fic to use some of those ideas.
Cupcakes was considered the most terrifying thing ever when it was first published. Ever since then, there have been an awful lot of grimdark imitators that make Cupcakes look mundane in comparison (Example: Sweet Apple Massacre) and now some people don't find it as scary.
Contemplate this: a show which has existed all of two years has an internet community so dedicated that ideas in fan fiction have already become accepted conventions and then faded into being boring. The conclusions you draw from this are up to you.
Cupcakes itself, meanwhile, was never as shocking to older fans who'd read the likes of Agony in Pink, Celebrian and Cloud Mows the Lawn, that it involved ponies being the only really new thing Cupcakes brought to the badfic table.
A Trekkie's Tale. Being the source of the term Mary Sue, people who seek the story out may be disappointed to find that it's extremely short, and a quite basic parody. Then you consider that it was written in the early '70s, when even the idea of fanfic itself was in its infancy.
The fact that it was parodying the very things that make up Mary Sue characters, which were already becoming common in Star Trek fanfiction back then.
Kikyo-Bashing in Inu Yasha was once considered somewhat of a comedic (or just refreshing) take on the character. Nowadays, a lot of people are just flat out tired of Kikyo-Bashing, some even going so far to see it as "unnecessary" or "annoying".