The internet is changing quickly, Stack Exchange is the foremost example of a new format on the web, and thus the traffic SEx.SE gets is shifting over time. As can be seen from a lot of the questions that get posed, ordinary people end up here, asking questions because they are curious about space in a way that dilutes its function as a resource for space professionals and serious students. Given that people will increasingly just verbally ask their internet devices a question and expect to be directed to an answer, the traffic of ordinary people, it seems to me, is only going to increase. Possibly a lot.
Stack Exchange communities have proven very resilient at handling such traffic, but it is generally seen as a problem and limited as much as possible. In the case of Space Exploration, the naive or confused questions that come in are mostly answered in good faith, and very well. Some don't make the cut and sometimes I think that is a mistake.
Being wholly funded by taxes, the entire fate of the field of space exploration hinges on public perception. The field has never had a tool for engaging the public like this site. I feel SEx.SE deserves a central place in the emerging network of resources for public education about space - places like the Space Transport and Engineering Methods wikibook, Wikipedia space-related articles (if they are substandard, shouldn't it be this community that sees that is corrected?), and other wiki-oriented things like Lunarpedia. I believe if SEx.SE doesn't draw the ordinary people who come here further in, so they learn more and their interest in space grows, it does the whole endeavor of space exploration a disservice.
So, it seems to me that perhaps some things should change so that mandate is better served.
First, if things are lumped together in the public mind, they should be lumped together here, too. Astronomy should be folded in. Planetary science questions should definitely be on topic. In fact, it might be better to call the community just 'Space', and drop the exploration part. After all, the field of astronomy is in the same boat space exploration is - if the public doesn't care, their projects don't happen. Pooling resources is the shrewd thing to do.
Second, A way of handling the extremely general questions of absolute beginners needs to be developed. I'd gladly tackle some of the questions that have been discarded because it would take a book to do them justice - by making a list of succinct points covering the basics, and loading the answer with links. Don't these people deserve to be pointed in the right direction? Some percentage of them will start reading through the linked resources and learning more. All of them will feel more connection to space exploration if they aren't given the cold shoulder. And especially - think of the children!!!
Third, a way to handle questions that have a certain degree of opinion to them needs to be found. Politics is the master of the fate of the field. Things that have no hope of being largely handled by factual analysis, sure, reject those questions. But some such questions really bear on where the field can go, and deserve attention. Maybe they could be clearly identified as being opinion issues, so that people keep that in mind.
The internet is shifting under our feet, Stack Exchange is young and has plenty of scope to adapt. Standards should be high. Scope should be broad.
Edit - I know I have broadly questioned aspects of the M.O. here, and I must admit to being deliberately provocative. These sites are run by experts, and experts sometimes forget what it is like to be a beginner, or undervalue casual interest. I felt if I was going to speak (I think) for those people, better to do it all at once.