I agree that effort is the main decider between a good question and a bad one. Since my thoughts seem to be very close to yours, this answer is essentially the same idea expressed differently. Hopefully it can also make this meta post more active, because it seems to have slipped right past me to be honest, while I think it's a very important one.
Good questions show effort, regardless of the level at which they are asked. Be it about a layman's explanation of black holes, a particular problem from a syllabus posing problems to a student, a random everyday phenomenon noticed by a perceptive/curious mind or a research-level pondering of a professional physicist. If the question shows clear effort from the OP, outlining the problem and their own thoughts, it's likely going to be a good question.
The only way such a question could still be considered bad is if it falls outside the scope, it's offensive, it's a duplicate (which can also point to low research effort) or if it's not a question at all. A question about some crazy theory connecting the female menstrual cycle to minute trembles in the earth's crust is obviously off-topic. A question à la "Pay only 500$ and find your perfect partner." is not a question and obviously spam. I won't give an example of an offensive question, but I recall there has been at least one incident in the past where a single user got very personal and offensive toward another user in questions specifically asked for this purpose. Obviously this is intolerable.
So: questions which show sufficient effort should, if I haven't missed anything, be easy to classify as either good or bad on the basis of other clear features. Questions which show little to no effort should be put on hold with a close reason pointing out the insufficient effort, with no mention of homework. Of course the homework policy can still be maintained, but it just becomes part of a larger idea, which should clearly shine through to people asking a question. This idea is obviously already present in the close reason for homework, but there should really just be a general close reason for low effort question. This way, questions like "Explain relativity to me" are also included - as John already pointed out.
To summarize: a question should not be categorized according to whether it is a challenge to the people viewing it, it should be categorized according to whether the person to whom it is a challenge has made sufficient effort in describing the what and why of this challenge and their own thoughts/attempted solutions. Copy-paste homework questions are mindbendingly irritating because of the copy-paste part, not the homework part.
The first way to make this idea of sufficient effort clear for all questions is to put it into the text on the right-hand side of the ASK QUESTION page. This should be editable since a little text about homework is written there, with a link to the meta post dealing with our homework policy. The second way is to change the homework close reason to a general low-effort close reason, which will include cases of low-effort homework.