I've also tried to create the kind of site you are hoping for. The key thing here is the ability to follow interests as well as people, but I think you are still getting bogged down in static categories. Look at how Medium has done it: Anyone can create a collection, and you can follow the collections (instead of following people). This way you empower people to curate and be rewarded for good curation, as well as allowing the followers to filter out the unwanted content. The classic example I like to use is I follow @gruber for his Apple commentary, but I don't care about Baseball, so a few times a year I wish I could filter that stuff out.
On the other hand, you want creators to be able to share seamlessly, and making them categorize their content isn't a good way to do it. Looking at the popular social services out there, making people choose a category is too much work, and is too limiting. And when you try to create a service that supports all of these needs, you end up with a really complicated tool that people don't use how you envisioned (see G+ - it has "pages" to support personas, it has private sharing via circles, it has communities, but you can't just throw all of this stuff at users all at once and expect a community to show up out of nowhere... you have to build your community)