About the plagiarism issue, there's nothing wrong with taking information wholesale if 1) it's not copyvio 2) it's encylopedic and suits the encylopedic context. I personally think that if anyone finds their text on Wikipedia and it was freely licensed or public domain, they wouldn't mind anyway, as long as it was being used well (that's why they released it under free license/public domain, no?), the only problem would be quality and copyediting for language, which can be fixed easily. After all, we do take things wholesale (with copyediting here and there) from the 1911 Encylopedia Britannica....and no doubt the article will evolve after that. If anything, it seems all the policies are sufficient. Copyright, manual of style, reference to sources, and being encylopedic. There's no need for a "plagiarism" guideline. If anything, any problems with plagiarism violates one these issues. If they don't (ie. like 1911 Britannica), then I see no problem.
Natalinasmpf