I realise this isn't your main intention here, but I don't think automated content would be a particularly desirable solution. Unless the sites your grabbing data have given you explicit permission to do this, you'll be flooded with DMCA requests which will significantly hurt your Google rankings.
When posting on a forum, the user still owns the content - they hold authors rights. What they're doing however, is granting the forum a license to publicise their work. The author still owns the content, and unless they've specifically agreed to allow your site to publish content (e.g. it was in the T&Cs of the site they signed up to), then you don't have permission to publish their work. That opens you up once again to DMCA takedown requests.
Even without DMCA requests, there are duplicate content issues. Google bots can't tell the intention behind a webpage, if a new site appears which is filled with duplicate content from other sites it'll likely believe it to be malicious and drop it out of search results altogether. Even without a malicious flag, Google doesn't display every site that contains search keywords. The original content site is going to take precedent in search results, and search engines may believe your site is a "print friendly" page or similar that it doesn't need to display. Potentially you could also hurt the SEO results of sites your grabbing data from. On occasions Google might decide your wiki should take precedent for content that appears on another site - a knock on effect is that the original site won't perform as well in search results. Even without any negative effects on the original sites rankings, you're still taking users away from another site. Site admins want users to visit their own site, not a third party site. You're gaining users from content from site A and as a consequence taking users away from the site the content was posted, who would otherwise have visited the original site.
That aside, from a users perspective you also don't want to be automatically grabbing content. If I sign up to site A - I've signed up to site A, and not a third party site. If I suddenly see that my posts appear on a third party site without my permission - guess what, I'm not posting on site A again. When I sign up somewhere, I don't want to be given a third party account on another site. But, if you don't do that then how do you credit the poster who wrote the content? Do you add the username? I don't want my username appearing on a third party site - if my username and my post is there, it gives the impression that I added it and am condoning the site. You would be using my name (however insignificant) and content to gain visitors to your own site, without my permission or knowledge. On the other hand, if you don't credit me - then you're just stealing my content. The intentions of a site may be as good as possible, but you'll become an untrustworthy site - as will the sites who are allowing you to copy their content.
Even small wiki's can take a lot of time and effort, but original content and manual submissions are the only way to go. :thumbsup2: