Well I can certainly understand that if someone stumbles across Music: Practice and Theory SE via a search engine such as Google, their first impression is going to be based on the quality of the question and answer they find.
Many of the questions and answers are excellent and would be useful to a large number of people who could potentially "Google" the subject matter and land on a great resource. That's what happened in my case. I discovered this site through a Google search and have found it to be very useful overall. Of course I have also seen many low quality questions as well as low quality answers.
Had my first impression been formed by reading one of these lower quality questions, then perhaps I would not have ever visited again.
Unfortunately, I don't see how we can possibly avoid having some low quality questions and answers. I think the best way to improve the quality of the posts on Music: Practice and Theory SE - is to encourage the active members of the community to be more pro-active in helping improve the quality by utilizing the tools provided to accomplish that goal. Specifically, down voting low quality answers, deleting inappropriate or potentially misleading answers, up voting good answers, editing questions and answers so they will make a better impression on the first time visitor and other tools available.
After all, this is primarily a community managed site and depends heavily upon contribution from the members to be successful. There are some members who regularly review the questions and make edits and leave valuable comments encouraging the OP to improve their question or answer. But more should be done to encourage these types of quality control initiatives on a larger scale. In other words, what can be done to enlist participation from more members?
I am fairly new to the site and don't know much about the history of what has been tried in the past. But one thing that comes to mind is if there was a way the moderators could reach out to some of the members who seem to have a history of high quality questions, answers and/or comments, and ask them to help in specific ways with the process of improving the overall quality of the content on the site.
Recognizing that would be asking a great deal from the moderators to take on that task by themselves, I might suggest that the moderators could appoint a panel of special deputy moderators in charge of quality control, who would be willing to participate and be empowered with the ability to reach out to individual members in some type of message system (or private chat) similar to what I imagine moderators can do now.
I feel we need to give these members an important sounding title to enhance their credibility. In other words, I know if a moderator reaches out to me and ask for help on an issue, I will have a higher probability of commitment due to the respect I have for them simply based on their title as a "Moderator". It's like "President", "Director", "Enforcement Officer", etc. Certain titles just command respect.
My suggestion falls short of giving these "special deputies" (or whatever title we choose to bestow) any other power, other than as it relates to direct communication with individual members. I would suggest that any members of such a QC panel, agree to participate in regular meetings in a special chat room where they could discuss the goals of the panel and ways they can use their position to help improve the site.
The first few meetings would be to define the mission statement and code of conduct and other guidelines that all could agree on. If you would like me to help organize such a panel, I would be willing to help.
I don't mean to suggest that such a panel would be solely responsible for the efforts to improve the content. Rather the panel would be tasked to recruit more members of the community to help with the process of improving the site by reaching out to them and asking them to help.