Thats the problem with a forum. After a time it becomes increasingly difficult to think up posts that haven't been done. Of your average forum population even under ideal conditions, you have maybe 60% lurkers, 10% occasional repliers, 29% active repliers, and maybe 1% new topic creators. You can get a higher topic creation ratio if there is some sort of statistical bonus or benifit to posting new topics (kind of like FARK greenlights) but generally you will only have a few people who decide to make new topics. Partially it's an ego thing, partially those people are just more direct. But even then, the average person will only make so many topics at a time, because most of them get self concious when there are too many threads with their name on the front page. So it becomes a dilemma. The faster the forum goes, the more topics they feel they can post, but the more topics that one person posts, the slower the forum goes because people get irritated by the spamming. Some people try the "post a billion topics all at once" route and occasionally, it works. But usually it backfires on the topic poster, so they post even fewer topics.
Over time, you begin to run out of topics, and even when you do think of new topics, you start to second guess yourself. "Didn't someone already post that?" "Is that too similar to that other thread?" "people will think this thread is dumb" etc. The truth of the matter is that if people don't like a thread, they will make it into something else so it doesn't really matter.
The situation gets even more complicated when one of your thread creators gets admin, since then there is a whole nother layer of doublethink on top.
Thats why I'm always on about getting new people into a forum. You don't have enough topic creators to sustain a growth pace. If I were you I'd have someone do some recruiting in the other game forums. Just know going into it that whoever does that it will backfire on you, even if in the end it is what helps jumpstart things, some people will see it as an invasion and will react negitivly.
Really, one of the best moves strictly from population density we could do is to re-merge OOT and Asylum.