What's the policy on old questions whose answers are no-longer current (but were correct at the time).
For example, this question: Seeking QGIS tutorials and web resources? - has a number of answers very highly rated. The problem is that quite a few of the links are pointing to outdated material now and don't relate to the current QGIS.
Is it worth re-asking the question seeking updated/current answers?
Or should we rely on users adding new answers to the old question? The issue here is that they'll never get upvoted and thus are less likely to be seen.
While @whuber's and @PolyGeo's answers are both very good, I still feel they don't work. I don't know what the "correct" answer here is, but these responses elicit several problems.
We can't make the "accepted" answer non-accepted, and the accepted answer is always at the top.
There aren't enough active members to down-vote all the upvotes of the now-incorrect leading answers.
We would be punishing the users who once had the right answer by downvoting.
The current incentive program (badges) is obviously insufficient for addressing this fully. For one thing a lot of them are /hard/ to get, even at bronze level, and require a very significant time commitment (or a lot of luck).
Closing them isn't a solution because then it's impossible to get new answers unless re-asking the question is allowed.
The site is heavily optimised to encourage new answers rather than substantially editing the content of old.
And probably the biggest issue of all:
For various reasons, only a small fraction of users will use/edit old questions and provide new answers. This means the question is only getting a fraction of the exposure it got when it was a new question; thus any new answers are likely to be suboptimal.
(This is also a problem with editing an answer).
Maybe the solution is to allow reposting of the question, but close the old one and stick a date on it. That way you've got a historical collection of answers and all are canonical for their period?