I'm not sure I completely followed eveything you suggested in your post.
However, a few points seem clear (from my point of view, at least):
1. Many of the longer threads have started with a "how could you do this with AOI?" question. The original question was almost always to do with a scene that someone was actually trying to model. So there was a specific point to the original topic.
2. I can recall many of those threads leading to contributions by others on both the original scene file (if it was posted), or with additional scenes. Some threads such as 'riding slug' have coalesced into a small collabative team building a much larger project (a small animation) than the original goal (a scene or just an individual character).
3. Very few of the discussions have been technical to the extent of being from the point of view of a programmer. Those types of discussions seem to live almost exclusively on the SourceForge Developer forum.
4. Most of the questions I've seen are more oriented to "how can I create this visual effect?" rather than "How can I apply this technique or technical feature?". My perception of these forums is that the former normally leads to the latter, and not the other way around.
5. Most (though not all) of the popular threads have involved a supplied scene or object. I think for many here, competitions which require people to create a complete scene from scratch require too much time that could be used in other existing projects.
From what DCrux has pointed out and from the points above, it seems to me that the best way to start a collaboration or competition in this community would be to state the challenge in a form something like one of the following:
1. "How would I create this effect?"
2. "How many different ways can we create this effect?"
3. "How would I combine these (multiple) effects in the one scene?"
4. "Let's all try to make the most imaginative use of this effect/feature"
Eg, Marc posted a competition or challenge on the use of ambient occlusion, which was really fun
5. "What effects can people suggest to spice up this supplied scene?"
6. "In which different ways could I animate this effect?"
I would not be a member of any club that would have me as a member
- Groucho Marx