When closing a question as a duplicate, it is becoming harder and harder to search for a good original as the pool of questions and answers grows and grows.
While the new dupe closing dialog is a huge step forward, it doesn't always work - if you've spent some time on the site, you know there are perfect answers to many new questions but you can't always find them. Or can't be bothered to, as your time is limited.
A way to further improve this could be introducing a vote for canonical answers.
It could, for example, work like this:
Answers get a new icon, the "canonical vote" (signified here by a cannon because I can't think of anything that makes sense right now.)
Only users with a certain minimum rep (maybe 1k+ or 2k+) see this icon.
The icon would work like the favourite icon: You can toggle it on or off at any time.
The hover message for the icon could read e.g.
This is a "canonical answer": It answers the question asked in the most extensive and general way, and is very likely to benefit other users with the same problem.
Questions that contain an answer with three or more canonical votes get special treatment:
They show up on the top in search results; maybe even under a special heading ("Questions with canonical answers")
They show up prominently in the "close as dupe" dialog (i.e. the canonical votes influence the metric that is used to determine the questions shown there).
There could be some rewards for users whose answers receive "canonical" votes - maybe a badge if ten of your answers get at least three canonical votes, or a counter of canonical answers in your profile. It would be really interesting as it's a badge that you can't game your way to, but this whole rewarding part is entirely optional.
Kobi's suggestions would be a great safeguard against over-use of this feature.
Dupe (but sans cannon):