Thanks for your input. I'll try to address your questions as separate bullets, with your question about "vision" as a larger paragraph since I think it deserves some thought and explanation.
As I mentioned to another user, I'm strongly considering getting rid of "Case of the Mondays" as it doesn't really serve a purpose anymore. The wednesday and friday weekly threads will remain.
The difference between /r/AskEngineers and /r/engineering is the type of content allowed. Here we strictly answer engineering questions, both technical and career type posts. There is some overlap since r/engineering allows those too. However, they also allow media, news, and blog posts (general content), whereas we do not. I started some discussion with the mod team over there on how we can avoid as much overlap as possible, but we currently don't have a solid plan for how to accomplish that (yet).
Posts that are good: I know I rail against highly upvoted threads, but if you look at the top posts from the last 30 days, those are all good. As long as people are talking about neat, engineer-y things, letting engineers use their knowledge to help random people on the net, and getting non-engineers interested in what we do... well, I'd say that's a good thing. I know that's probably not as focused as some of you might want, but I'm open to suggestions on how to refine the scope of the sub.
The "vision" of the subreddit is the million dollar question. I didn't create r/AskEngineers so I can't say why it splintered off. But to answer your question, I envision it to be a place on the internet where engineers can answer questions similar to eng-tips and engineering.StackExchange, but give up some of the stiffness and formality of those two places in favor of openness and wider discussion.
One of the things I try to be careful of, especially when I have to get heavy-handed with comment and thread moderation, is to avoid being too strict; otherwise I would kill the open atmosphere that is otherwise not present in both of the forums I mentioned. No one cares if you curse a little or make cheesy engineering jokes on reddit, and I think that's a good thing. At the same time, I do encourage everyone to keep both eng-tips and StackExchange in mind when they need a question in a specific "style" (for lack of a better word) answered.
In terms of what I'm aiming for, the obvious answer is AskScience... however I also have to say AskHistorians. "But that's not even a technical sub!" you say. This is true, but I'm going for the essence of things here. In AskHistorians, the answers are really deep and contextually relevant, there's a lot of "thought chaining" (i.e. comments build off of other comments), and the discussion is just super high-quality regardless of the question being asked. I feel that AskEngineers hasn't even come close to reaching that level of quality yet, but at least we have a tangible goal to aim for.