It seems fair that if people upvote the question, they signal that they also don't know the solution and are interested in the answer.
If a question is upvoted, it means that people thought the question was well-written and/or interesting. It has no relationship whatsoever to whether or not they know the answer.
I've upvoted several questions that I've also answered. I've downvoted or voted to close one or two questions that I've answered. I've even upvoted several questions that I probably could answer but just didn't have the time/patience to dig into. If it's a good question, it deserves the vote regardless of how many answers it has.
Questions without upvotes, might very well be niche questions only the OP is interested in.
Or they could simply be technically challenging questions that the majority of users couldn't be bothered to read/understand in full, and people only upvote questions/answers that they understand.
On the other hand, heavily-upvoted questions tend to be of the bikeshed/subjective variety, such as this one on the front page now: Why open source it? And how to get real involvement? The question's mostly rambling about bugs in some open-source JS library, it's barely even a real question and already has 3 close votes (I'm debating whether or not to make it 4). No offense to KR, but does the top answer - which basically says "yeah, every project should be open source!" and is likely to also become the accepted answer - really become a better answer because 6 people upvoted the question?
Should the accepted answer to this frivolous interview question be worth extra because of the question votes? Is this solving a useful problem?
Your so-called "niche questions" are what Stack Overflow is all about. Being able to ask almost any question and get a decent answer. If you're interested in answers to very popular questions then you don't need SO, you can find your answers with Google. I'm not against them being asked on SO, but I'm certainly against them being favoured more than they already are.
Heavily-upvoted questions already attract a lot of answers. What we need, if anything, is a way to attract more attention to the less popular questions, and - what's that you say? We already have a bounty system? Oh, never mind then.
If you have a great question that doesn't have a good answer, you can start a bounty, paid for with the rep you accrued from having such a great question. I'm 100% opposed to any initiative designed to attract more attention to questions that are already popular; they're already too much of a self-fulfilling prophecy.