I don't think that judging question quality should factor answers at all.
A good / upvote-worthy question should satisfy most if not all of the following:
- Is the problem clearly stated? We shouldn't need to derive the question parameters based on answers.
- Is the expected outcome clearly stated? We shouldn't need to read the accepted answer's output to understand what the OP wants.
- Do the title (<-perhaps most importantly considering search engine listings), body, and tags make it easy for researchers to find the page when the page represents the problem that they are researching?
- Is the question unique? Stack Overflow probably suffers most from site bloat due to dupe posting, which consequently drains valuable volunteer resources.
- Is there some indication of research? (e.g. "these pages are close, but...") This is super, super easy to prove by dropping a couple of relevant links. When linking to SE network pages specifically, this binds related SE content (win), serves as an aid to researchers by offering additional questions to chase if the current page is deemed unsatisfactory for their issue (win), and informs volunteers generally about your level of understanding (win). A possible symptom of insufficient research is the inclusion of inaccurate terminology in the post. Using correct wording makes the question easier to comprehend and improves searchability.
- Is there context? While answers should endeavour to accommodate a general scope, context ensures that answers can conform based on sample input so that researchers can differentiate answer quality more easily.
- Is it on-topic for the community that it is posted in? Off-topic questions, even if interesting should never be upvoted.
A question is not good merely because it can be answered.
A question is not bad merely because it has not yet received an answer.
There are heaps of Stack Overflow questions that are ~10 years old that only satisfy 2 or 3 of my above criteria, but have hundreds of upvotes. This sends a bad signal to new question posters -- they see these old questions, and think that that is the expected standard.
If a posted question only satisfies a moderate number of the above bullet points, it is a "neutral question". If it can become an upvote-worthy question, inform the OP of what is missing and/or suggest an edit.
If a question struggles to satisfy most of the above criteria, then I reckon it is downvote-worthy. A downvoted question can very possibly attract lots of valuable answers, but that result is irrelevant to judging the question's quality.
Whether or not a question is "interesting" can be safely deferred to pageview count, star count, and possibly the volume and quality of answers that it attracts. I don't believe that "interesting-ness" should be part of the evaluation.
Personally, I have a bias toward deeming questions as neutral. A question needs to be really good to get my upvote and really bad to get my downvote. This results in the community feeling relatively welcoming, while calling trash "trash", and rewarding the posters that employ due diligence and bother to craft exceptionally awesome content for SE.
I also don't automatically downvote a question for being a duplicate. If the OP has obviously toiled to craft a good question, but just didn't know where to look, I'll vote to close and make no up/down vote.