Good topic! Search in forums is a really tricky thing, and the solution of using Google tends to come up a bit too often for my tastes.
Would agree here. You don’t want old topics to dominate your search results.
Judging from my own search expectations, I would want the best results to be threads that are both recent and active, and which are a good match in terms of title and category. And even after that I would prefer recency to have a notable impact, because I often search for things that I vaguely remember.
Unfortunately also true. Personally, I’m not even sure how much links would really contribute to relevance (though they probably would be a factor), because in the forums I’m active in, but which are not support or technical forums of some kind, linking is relatively rare.
So I tend to consider recency and activity, i.e. number of views, likes/reactions, replies, within the not-too-distant past more important (not if this is also factored into the current search implementation or not).