I've had people tell me quite frankly, "Will you please stop writing about $£&%ing VAMPIRES!?" A lot of other people have been less forthright about it, but the clues are there.
"Wow!" Laughter. "You're writing a lot about vampires recently." Or teasing, when I tell friends that I've just posted an article, along the lines of, "Is it about vampires, perchance? Is there yet another avenue left undiscovered?" Or the very subtle, "I did used to like it when you wrote about history, human rights and things."
As time went by, fewer random people stopped by to comment on my articles.
In short, not one person has openly embraced my saturation of vampire articles. Nor has anyone uttered the praise, 'Hallelujah! You've finally started writing within a niche!' In fact, everyone waffling on about niches has gone strangely quiet in my digital earshot. (Except for the individual who proffered the opinion that, if I was going to write niche, I should have used these articles as the basis of another profile on another site.)
There were plenty of comments (publicly, privately, in comments, on the forum) about Pets and Animals not being the right category for vampire articles. I was writing so many, that the furry critters couldn't get a look in. The infestation eventually led to the whole legendary creatures sub-category being shifted over to Culture and Society.
I'm guessing that the Wizzley team, and every author involved in having to relocate their articles, really loved me right around then. Though they took it with good humor. I also managed a hat-trick in having all three of the Wizzley team members recommend/request that I change something. There was a definite sense of damage limitation going on, or me being paranoid. One of the two.
In fact, the only immediate good result that I discerned (give or take the discovery of True Blood) was the depth in which you can write within a niche. The more I delved into the subject, the more I found correlations between sources or noticed how x had been inspired by y. There was nothing superficial about the later historical and folklore articles.
Ask me about vampires. Anything about vampires. I feel like quite the expert after all that.
As for traffic, that's remained just as constant as it did when I was scattering my articles across many topics. No huge surges, but first day readership showed no massive slump or rise. It's too soon to tell on the long term effects.
My personal take on it: I'm not at all convinced that niches are all that. I've been given no evidence - beyond the fact that you can become very learned on a particular topic - to believe that writing within a niche is particularly wonderful. Though I did hear a whisper that Google has loudly hinted that it prefers to pigeon-hole writers into their niches, so they can more easily promote or blast them in the SERPs.
Sounds more like a reason not to be a niche writer to me. Unless you really are the greatest authority, on the entire internet, for your subject.