Knowing who and what your site is for is key.
As important, is knowing who and what your site is NOT for.
Consider this site, there are lots of things I can and do talk about, but in most cases I try to bring it always back to the main themes of boosting your authority and business via new media.
Pictures of my cat are more likely to appear on my personal site. Photography stuff goes on my photography blog.
What about when a topic does have relevance to your audience, but only a small subset?
That is when segmentation comes in. This is where you get people to opt-in to a more focused site, list or feed, so that the rest of your audience are not bothered by it and where you can comfortably lavish the full package on just those people.
Sub-lists though are not the only way to do it. You can create off-shoot websites, as I did with Authority Blogger. These satellite sites can attract their own search traffic through creating highly targeted content and some kick-start links from your main site.
This traffic will also be funneled to join your niche email list or feed, and will not be distracted by your broader content outside of that silo because they will not get to see it unless you intentionally link it up.
Yes, creating new sites is additional work, but often a highly focused site does well both with audience and search, much more easily than a broad, cumbersome and disorganized monolithic site. A domain and ten pages of killer flagship content might be all you need.
Worth a try?