Lots of good notes already here.
The scale of this issue matters, if it’s 1% of your site it’s probably not an issue. If it’s 40%, then you have more of an issue.
You tend to “deal with” these sorts of posts not because they’ll improve the link flow around your site, but because you’re trying to raise your sites general quality (i.e. you want your site to be viewed as high quality in Google’s eyes and not have issues with thin content, panda issues etc.)
(In theory if you were to redirect or canonical or them it could change your link flow, in practice that’s hard to measure, probably having a minimal effect and not the reason to do this.)
My general decision tree would be something like:
- Is this a high quality searchable question that isn’t answered anywhere else? I’ll try and get someone to answer it.
- Is it a high quality question, but answered elsewhere? I’ll try and consolidate it with the other question and get that one to rank.
- Is it a low quality question, on a unique topic? I’ll try and get the questioner to improve the question. Otherwise:
- It’s a low quality question, that can’t be improved or is on a topic that’s already covered. I’ll no-index it.
In practice depending on the size of the site, you often have to use automated thresholds to work with these things (i.e. less than 30 words, by a first time user etc.) and it’s very much a matter of experimentation.