Auto-search/suggestions for forum posts
Some job ticket systems do an automatic search when new posts are added, to suggest previously-created answers before submitting the post. I don't know if Vanilla has a plugin to do something similar, but if so it might be worth you putting in, and having it search the forums, current known issues page, and maybe Trac. I notice an awful lot of reposting of the same old questions, and such a thing might save those who are "answerers" here (you know who you are) a bit of time.
For example, forums.dklab.ru experience tremendous amount of repeating posts, so they had to put:
1) search boxes in every corner of their pages.
2) topic suggestions for 'add post' form using keywords which user types in the post title and the post text.
3) and even short quiz to filter people who cannot formulate questions in correct way :)
Their search works without reloading current page, which really helps to find a correct topic posted earlier.
It is not always so easy to find a topic with exactly my question, especially if I don't know for sure if it exists. I hope zotero.org will have something like that soon. Thanks
There's also a LiveSearch plugin that might be useful, though I haven't seen it in action.
It'd probably also help to combine the Topics and Comments modes of the search.
Some prompting on the 'start a new discussion' page, accompanied by a prominent forum search form and links to the FAQ and other documentation, might help.