When is it still appropriate to use Community Wiki?

What I find specifically problematic is the 'guidance' you put at the bottom of each of these questions:

• This is not a question that has a single correct answer, so it should be a community wiki.
• Please provide exactly one suggestion per answer.
• Please upvote and downvote answers according to your experience.

First of all, there is never any single correct answer to any parenting question, except perhaps "should I kill my children?" ... and even then, I am torn.

So the first bullet is completely superfluous -- the fact that you are on parenting by definition means everything is subjective and nothing is definitive. The third bullet is also redundant; do we really need to remind people to "vote based on your experience?"

The biggest problem here, though, is that the call to provide "one thing per answer" is extremely dangerous. That more or less directly leads to the Infinite List of X problem. Instead, you should remind answerers that answers be complete, clear, and most importantly per the Parenting FAQ -- backed up!

Please note that opinions shared here should be backed up either with a reference, or experiences that happened to you personally. Also, posts that primarily exist to push a specific agenda (propaganda), and soap-boxing, are not welcome.

Giving them the easy out of

"I see, all I need to do is list my favorite little thing here and let people vote on it!"

... is sending the wrong message. Instead, they should be thinking

"Uh oh, I need to explain why and share my experiences here -- and also defend my position with research and data!"

What we're looking for in a good community wiki question is not a shopping list of ingredients, but a set of answers that explain how and why in some detail. If a question is getting short, throwaway answers -- edit the question to be more clear about what is expected.

It looks to me like you snuck in some poll questions under the guise of community wiki in both the examples above.

Poll questions are perhaps the worst type of questions on our engine.

For example:

What is the best name for a boy?

Sure, it's fun, and it may have some interesting answers, but essentially you are soliciting lots and lots of answers.

• What happens when suggestion 765 for a boy's name pops ups, how is it ever going to displace the top answer?
• Who is going to read through 765 suggestions from names?
• How can I see a simple graph breaking down the information?

Our engine shines when there are a limited number of answers, take limited as 1 to 10. If your question is soliciting more than 10 answers odds are it is not a good fit for our engine.

CW is not going to suddenly turn it into a good fit, it was a bad fit when it started and a bad fit after it was turned to CW.

As to your questions:

Provided that the question and answers remain on-topic and valuable, is CW still useful in cases where no answer is (or can be) "better" and "more correct" than another?

I would argue that no, it is not. Opinion can be backed up. The person answering "Read a bedtime story." could back it up with some research or books on the subject. When you strip reputation you strip the incentive to improve any of the content.

Why would a person bother refining and backing up their answer?

Should moderators actively set CW on such questions, or should the system be the only entity allowed to do so?

I am not sure. It is hard for me to think of even a single instance on an Stack Exchange 2.0 site where a moderator needs to step in and do so. The main reason is perhaps site scope change.

Over the years Stack Overflow changed its scope and we are stuck with a bunch of legacy that would not have crept in these days. Dealing with our legacy of doom can be somewhat tricky.

Prompted over the weekend, I posted an example of one of the only questions I think is a warranted use of community wiki. Look it over and understand it - a general FAQ, not a replacement for more specific questions (Apple's problem as mentioned on the aforementioned blog post). It actually has community contributions to shape its answer. And it is, of course, a valuable question.

Provided that the question and answers remain on-topic and valuable, is CW still useful in cases where no answer is (or can be) "better" and "more correct" than another?

No. I even put a specific point in there to address this, and the example from Gaming helps illustrate this. That said, be careful not to overgeneralize when looking at the essence of a question. The examples you've provided have some of their own issues, which we'll look at in a bit.

Should moderators actively set CW on such questions, or should the system be the only entity allowed to do so?

If "such questions" refers to the above scenario, then no, again. If by "such questions", you mean questions where it is appropriate to use community wiki (which is rare), then we are given this exception handling tool for exactly that - exception handling. So, on to that point...

I'm not sure how to decide this, and not sure whether CW should be actively applied.

Parenting is a bit of a different case, not unlike Programmers in which their questions are intended very much to dance on the line of "subjectivity". But remember, subjectivity is not our enemy, not unlike how community wiki isn't something to be loathed. It's abuse of both that is what to be loathed.

Your example questions, are polls, not questions, and even for a subjective site, that's not all that useful. A more pertinent blog post for this is Real Questions Have Answers, which can be applied even to a subjective site. Looking at the bedtime ritual post, it's simply a survey of an item per post. I cannot look at any single answer and say "This is a solution". They are all parts of a solution.

The point of community wiki isn't for a bunch of people to contribute one-line points as separate answers - that's rather the opposite. You want the conglomeration, the full package, to occupy a single post. If it's scattered in several posts, that's where your voting and paging and all that is hurting you. Questions should be having answers, not "the answer is the combination of all the responses here". That is the difference between "What software exists to record my gameplay" (all answers are "equally valid", the "solution" is the set of answers) and "How do I record videos of my gameplay?" (any individual software is a solution).

When it comes to questions with multiple possible answers, I recommend this rather old but still valid post I wrote for Gaming Meta. Pay special notice to the fact that community wiki isn't so much as mentioned in that post.