That was my understanding as well; that it would effectively work just like GChat (where spam certainly exists, but is a trivial problem).

TFAuthor dismissed that as a non-option, because it would make Wave unsuitable for collecting unsolicited feedback and sales contacts.

But it seems to me that a single Wave account that auto-whitelisted contact attempts would solve that problem at the cost of reintroducing some capacity to spam, but at a vastly reduced level.

Simply applying existing tools and leveraging the other benefits of Wave over SMTP would seem to seriously marginalize spam as a concern.

If you have to accept me as a buddy before I can send you a wave, this will prevent spam but make it harder for wave to replace email. Incidentally, this is also why "solve this turing puzzle before I accept email from you" type of anti-spam solutions are not widely accepted.

Agreed. One way to prevent spam within Wave will be to limit its use. That could be done by explicit whitelisting and an out of band communication to get whitelisted (such as using email). Or just by limiting Wave use to people I actually know.

All unsolicited communications could come via email instead of my Wave.