I have a tendency to randomly jump into a new niche that I know absolutely nothing about a couple of times each year.
The last topic I choose when I went wild were “bible studies”, and before that it were “Chinese antiquities”. So far these sites has been a huge waste of time, however, I have learned a couple of pretty valuable lessons fx. how to find expert writers in any niche.
There are scores of PHD students and other experts, who are just dying to get someone to publish their articles. This means that if you create a good looking site and get a bit of traffic to it, you can simply post a “experts wanted” ad on your site, and they will contact you.
These people won’t be writing promotional stuff for you, however, they can write incredibly good “how to” articles and guides. In addition, they will be very likely to go out and build links to your site, since they want people to see that someone is publishing their articles.
The best thing is that these people will be okay with being paid 20$/article, as long as you make sure to point out to your visitors that they are an expert, and since that raises the perceived value of your site, I have been more than happy to do that 
In addition to being good writers, these people can also be a big help when doing keyword research and figuring out what to promote. A question like this one can really give you some amazing information:
“I’m having trouble finding advertisers for the site, and since you know much more about the topic than I do, I were wondering if you know about any really popular and/or expensive products that I may not know about”.