Great ideas here, but I'm still voting for putting up wiki site as a starting point. Developing something more sophisticated later on won't be much of a problem, but IMHO what we need now is first version - and we need it pretty quick, so that we can see how it starts gaining momentum.
When discussing the platform choices, keep in mind that most wiki platforms are exceptionally good at handling stuff like multiple editors, access restrictions and revision history - absolute necessities if we're going to have more people producing content. My experience comes mostly from MediaWiki, though, so that's what I'd suggest. It's ugly and kinda bloated but it does get things done
@charliez, that sounds great too, but wouldn't it provide some extra credibility if wiki site was running at manual.processwire.com or something similar? Though I'm not sure if this was what Ryan had in mind..