I think there are people who'd like to contribute to the forum but aren't sure what to add. A common (and reasonable) view is that there are already so many important ideas to read, so you should only add to the pile if you've got something truly worth posting.
To offer clarity to people wanting to contribute to the forum, input from the community is best: What is worth posting? What posts does the forum benefit from? What posts does it need more of?
To get the ball rolling on this discussion, I'll pitch in some trends I've noticed (although might be completely wrong about!)
The following seem popular (at least lately):
Perhaps more cost-effectiveness analyses?