Do the benefits outweigh the problems?
In my opinion? Conditionally... yes.
I think the idea of what wiki should have been has been bastardized.
What Wiki Should Have Been:
"Community wiki" should be rare. If you agree that all questions on the site should be answerable programming questions and not subjective discussion, then where wiki comes into play is that rare situation where the question is answerable... but the answer is built up by group of people.
An example where wiki could work:
I am working on a C#.net team doing A, B, and C. My job is to author a style guide for my team. What should I be sure is include in that style guide?
Since the "answer" will ultimately be a collaborative work, each contributor is, in effect, relinquishing individual ownership of the answers by contributing to a larger body knowledge. That's wiki.
What Wiki Has Become
- I have a question that would be closed but, if I make it community wiki, I might just squeeze it by.
- I have an answer that will probably be down-voted, so I will wiki-fy it so it doesn't affect my account.
- I want my "accept rate" to be higher so, if I don't find an acceptable answer, I'll just make my question community wiki so it isn't "counted."
- We need a way to disconnect a post from the reputation system, for whatever reason. Too much editing? Wiki. Too many answers? Wiki. User's going to get more reputation than warranted? wiki.
If there needs to be a mechanism where reputation is no longer appropriate, maybe we need another term or mechanism to facilitate that.
Just my opinion.