The title says it all.
Voting system is not an option as it works against interesting questions, just because most of folks have no idea of the matter.
Say, there is a question like this one: How can I avoid getting a 502 Gateway Error while restarting php-fpm?
It will scarcely get +1 or +2, while yet another "Headers already sent" will get 10+ as it's familiar for the masses.
So, I suppose it will get less relevance with search.
I think there is no way, But it's really important thing, I think. Number of questions being increased and every day it become harder to find a diamond among the rust.
Every other collaboration society ends up with creating some sort of FAQ system to reduce number of repetitive questions, but such practice seems against SO ideology and profits.
May be it would be possible to make some Superupvote button, making +10 at once? Costs you -5 to prevent frequent use and available for the 10k+ guys only?
Or, going even further in dreams, if it possible to make some "goodness mark", to mark good questions with good answers ("headers already sent" kind can be marked too of course), directly adding to relevance?
Such an improvement will help to solve stackoverflow dualism - it pretends to be a source of knowledge but in real it turns out to be heap of garbage + online chat.
It's ok with chat but I wish there was some distinction between programmers questions and repetitive chat logs in the search results.
Or well, it can be put this way:
I'd be interesting not only in answering questions but also in reading interesting ones too. But there are literally thousands of repetitive noobish questions and it's just impossible to pick pro ones off the stream.
If there was some mark, or separate feed, something named like
pro.stackoverflow.com, it would be great to read like news feed. With 10k limit to press the button of course.
Long story short: I wish Stackoverflow was not only kind of automatic answering machine, but also indeed source of some knowledge.