we're thinking about how to add categorization to jig, so i am thinking about this a bunch.
There is a disincentive to using a more generic subject and broadcasting out-of-context on Subjot, which is that people unfollow you.
I saw one user doing that in our private beta and I unfollowed him, since the entire premise of Subjot is having a feed of stuff that is interesting. We have a very unfollow friendly culture, so it's not a faux pas to unfollow a subject that you don't find interesting.
It is not a one size fits all solution but it has been working for us. Just like you wish you could unfollow your friend who live tweets the entire episode of Gossip Girls, on Subjot you can easily unfollow specific aspects including a broadcast subject.
i feel like you will have to have aggregate topic categories (everything about topic x) to get enough traffic in that topic. remember that there is typically a 10:1 reader:poster ratio (or more!) and that is what will get spammed.
my gut sense is that if you make topic directories for people to sign up to you are adding transaction costs to get people into the system.
i'm not at all sure what the solution is, though.
on cluedb i made it so that multiple people had to use the same tag on an item before it showed up. cluedb has approximately zero traffic, however.
Alternatively allow people to vote on tags? Adds complexity to the UI, but it may be possible to keep the buttons subtle but discoverable.
We have been playing with some ML/NLP type stuff to cluster subjects that are the same. So we can tell if your post about Football is actually NFL or Premiere League... but we're a super small team and its a bit to early to put that stuff into production yet.