I suspect it wouldn't work -- due in some part to vanity, and in a large part to the well established social-psychological phenomenon of "social proof." As a species, we like things that are popular. Conversely, we are hesitant to sample things, let alone subscribe to them, until they've been validated by others. Ideally, we seek things that have been validated by others of high social status. But in a pinch, validation by a large number of people will do the trick.

We keep social score. And, even if we don't consciously realize or even accept it, we want others to know our own score.

I tend to agree with most of your points, though. As you very eloquently put it, our natural tendency is to accumulate noise -- even if we claim to want signal clarity. Google+'s circles are a great attempt to let us have our cake (noise) and eat it, too (signal). But over time, I imagine that the act of constant social curation and message-filtering will grow more tiresome than it's worth for many users. That's just a hunch, and it's totally unsubstantiated by any data I have, or could ever hope to get my hands on. At least for now.