Niche content is what will get people to your website. If you are an expert, then let the rest of us know how to do what you do. A lot of talented people waste their opinions on forums. That's not to say I don't appreciate their help, but if you're good at something and have answered 100 or even 20 questions on a forum, you could have answered those same questions on YOUR website and driven business your way, all without having to worry about who owns the content. That said, your niche can change, even on the same website.
One client of mine wanted to sell organic goods, but then she got into house design. She has a domain name with Organic as part of the name, but why wouldn't that work for organic house design? Maybe you'll need to change your meta description, but if you're writing about organic house design and have little competition, people will find your articles. Mostly, you have to write them.
I have a website called Satisfamily that is about being satisfied as a family. Some might think it's too vague, and it probably is, but it's been around enough that search engines pick up the diverse content, even as I change the stories from being centered around Milwaukee to Kansas City to Jacksonville, FL, as my family moves. And when I find the right niche for an article, it doesn't matter that I'm writing it on a website that once talked mostly about Wisconsin. For example, I wrote a couple of articles about a housing and gas station development going up in my neighborhood. I questioned whether the people buying into Magnolia Grove near Kernan and McCormick in JAX would want a new gas station right on the corner. No one else seems to be asking the same question, so the articles I've written rank well with Google. No, I'm not trying to sell something, but it shows that if you take a very targeted idea and run with it, you can get the hits you want to either sell something or at least get your opinion out there. Even though I was told once again today that it's all about the money, I figure it's also about the public opinion, and your goal in niche content writing is to affect public opinion.
I'm currently writing an article that will talk about Milwaukee's new Rapid Bus Transit experiment. And I have one about injustice when it comes to the police in Johnson County, KS. If I posted these articles on local newspaper sites, they'd get more hits by far, but those hits would be for someone else. Sometimes, it might be worth doing it that way, like for my friend who sells a product related to Chromebooks. He can post on Chromebook-specific forums about his product and hope the readers look for his item. That might be just as effective as writing an article on his own website, since it's a business website with the purpose of selling that item.
Either way, if you write good content, people will read it. Even if you're selling something, you might want to give an honest evaluation of when people can do without your product. Or just talk about the usefulness of a related product. Like if you were selling a line of designer backpacks, you could talk instead about cool gadgets that kids might want IN the backpack. It's just more interesting than article after article about your wonderful backpack.
Give it a try. Change the niche to something else on your website to see if you can get readers from other areas that interest you. Those people might be interested in your lawn service or they might want to just get free advice, but they are at YOUR website. Then you can tell them your thoughts on somewhat related topics. You're adding to the conversation, anyhow, and that's a pretty cool side-effect of this whole internet thing.