I haven't posted a lot of public posts, I mean - and that's because the idea of G+ circles almost discourages the idea of public posts. If you have friends with different interests, almost no topic is going to be of interest to all of them. Having written that, though, I am suddenly wondering whether I have been misusing extended circles when I should have been using Public. For Joe User, who doesn't have a lot of unilateral connections on G+, and has no personal brand, Public is worse than extended circles if other people's comments inherit that level of privacy because other people might not wish their comments to be public; or if they restrict their comments so that they are not public, it will lead to a disjointed public archive of the thread. Neither is good because what G+ is excellent at is delivering more detailed discussions and conversations from people that you may not have known (or even know exist) who have something valuable to say. Actually not only that, if people have added you because they share a very specific interest known to both of you and they receive not only the specific posts you intend for them but also ALL your public posts which are NOT about your shared interest, your signal to noise ratio for that person drops badly and they may want to de-circle you (did I just coin a new expression?).
Phew this post turned out much longer than I had intended on a smartphone! (although Ultra keyboard for Android does rock…). All of which cannot be addressed without the API allowing providing circle-level authorization by the user, although perhaps it can be worked around by having a public user and a private user account; add your public user to a circle called 'public'.… hmmm, I think I'm going to have to think about this a bit harder and run some experiments!