Perhaps there is an example or demo you could make public, to give less adventurous visitors (like me) an idea of what it does? (edit: like the /gauss link I just noticed - now I like it)
I'm all for stealth but IMO this is too stealth.
We reasoned that the signed-in experience is a lot richer than what we could show signed-out on the landing page, but perhaps we should not take it to such an extreme :)
Building a bad community, not setting precedent, training up people and solidifying a culture are pretty lethal to your stated goal.
Once you are open to all, your constant battle will always be:
1) Not let the Signal to Noise ratio degenerate 2) Be able to split the Signal down into sub categories for people to process, as opposed to a torrent which then leads to arbitrary discarding of significant data.
With regards to managing signal to noise: 100% agree. Figuring out how to slice and dice the content so that you see what matters to You is our number one "tactical" objective. It is actually a hard problem, but one that gets easier as you come to understand the content being created and once you can benefit from enough liquidity to slice and dice at will.