Determining Gwen Stacy's exact influence on superhero comics is actually made more difficult by the fact that superhero comics basically whitewashed the shit out of their harsher Golden Age excesses in the Silver Age, since Batman originally carried a gun, and Superman originally fought battles in ways that would make the Authority seem subtle and restrained.
It becomes much simpler if you regard "everything from the Silver Age" forward as basically being its own THING, since in many ways, those Golden Age superhero comics were still outgrowing their pulp novel roots. Once you do THAT, then Gwen Stacy's death actually has a much more strikingly clear influence - not only is she the first "fridged female," but her death is also arguably the birth of the whole "grim and gritty" era of superhero comics, well before Moore or Miller, because Gwen Stacy's death - even if you include the Golden Age - represents the first real, clear, conscious injection of FATALISM into the genre.
At the time, this was revolutionary - hell, even a couple of decades later, it was still revolutionary - because the entire point of the genre, up until that point, had been that Heroes Ultimately Win (even Peter Parker's mixed fortunes were meant to be seen as improving over the long run, albeit slowly and painfully), but once Gwen Stacy's neck went SNAP!, it was the first time that, in a big and important way, we were shown that the hero was fucked, no matter what he did.
And here we are now, roughly FOUR decades later, and things have reversed themselves so completely that it's now all-too-rare to find a superhero comic that DOESN'T send a message of We're Fucked No Matter What. Which makes it weird that Joe Quesada wanted to retcon away Gwen Stacy's death, because in every other way, he and Dan DiDio have turned Marvel and DC so dark that the goddamn Watchmen seems uplifting and hopeful by comparison.