On the anecdote side I do know that within the past couple of years I saw a discussion on here about how many visitors someone gets from a top of the front page on HN. The numbers were absolutely miserly compared to what I experienced getting the same repeatedly years earlier. Like, 1/20th or less.
Maybe it's just HN that declined, but if so where did the tech news community go? Digg? /. Reddit /r/programming (to some degree yes for the last one, though still it is nothing compared to what once was).
Everything is much quieter and more restrained than it was.
And sure, there are time zones circling the globe. But generally on the English tech sites, the US/Canada are going to dominate the demographics and have an outsized effect on spikes.