You might find the article The Future of Community Wiki helpful. Some relevant snippets
The intent of community wiki in answers is to help share the burden of solving a question.
Community wiki is like a cheese knife: it is a specialized tool to be used sparingly.
Community wiki is for that rare gem of a post that needs true community collaboration.
My interpretation of that is that community wikis are not there for me to write a partial answer and have other folks to fill it in instead of writing their own answer, or for me to take a comment left by someone else and post it as CW answer so I don't get reputation for it.
A CW is appropriate when a complete answer to a question is a large effort that would benefit from the community working together to fill out and refine it. A good example is this canonical answer on ELL. Another situation where a CW might be appropriate is the subject matter is controversial (but on-topic) and voting is likely to be emotional. The wording of the answer might need to be refined to be as neutral/objective as possible. The problem with that is that there could be conflict among the editors that isn't particularly constructive.
In my opinion, using CWs for reputation consequence avoidance is counter to their purpose. If a comment can answer a question thoroughly and well, the question isn't a very good fit for the SE model. It shouldn't be difficult to take a comment and flesh it out by adding supporting references and discussion. When you make the effort to expand the comment-answer into a real answer, you deserve the reputation that comes from it. This isn't a quiz show where the first person to buzz in gets the points. If all you're doing is copying and pasting a comment into a CW answer, I think that's bad practice that places statistics and rules over actual value.
If you want to write a partial answer, just say it's a partial answer. If the community strongly dislikes partial answers and down-votes them ruthlessly, then the solution isn't to avoid the reputation consequences by making a partial answer a CW. The solution is "don't post partial answers". If I felt the community was opposed to partial answers (which I think are OK), I would come to meta to try to change folks' minds, not post them anyhow and try to nullify the primary mechanism the community has for discouraging things outside of the norms that they've settled on.
I took a quick glance at the highest scored answers in a list of community wiki posts on EL&U and I remain convinced that CWs are rarely needed.
So I got some help, and Rene worked out this query for CWs with multiple editors. I haven't looked through the data in detail yet, but thought it might be interesting. Of the 577 wiki answers on EL&U only 87 of them have multiple editors.