You bring up an interesting point. "If the question as such doesn't add value to steemit, why should I upvote the question?"
But it then begs the question : Who determines if it is a value? It might not be valuable to you, but it might to others. It probably was to the author of the post. Therefore couldn't it be valuable to others in the same mindset?
For example, the other night I saw several posts, asking how to insert an image in a Steemit blog. I responded with a link that had a good explanation. I was not seeking any up-vote, nor did I get any, I was just doing my community service. The answer, which has little value to most of the community, was needed by the author and likely others who will follow in their footsteps.
So, who is to say if responses to questions are valuable or not? It is an interesting question. I think if I post a question and get a good answer, I would likely up-vote the reply (at least the first one who answered my question)
That's why we don't have a single judge here but a voting system instead.
Good/bad/valuable/junk are all highly subjective. Just do what you think is right, and thanks to decentralized voting a result will be determined.
Are you recommending we have a broader set of voting options? We have an up-vote and down-vote already. Perhaps NSFW, Spam, and Dangerous (or some other combination) to better express our views or warnings-to-others which can be tabulated as part of a voting system? If so, I like your idea sir/madam!