If you'd like your online community to be the "go to" destination, you need to offer the most authoritative, the most expert, the most interesting content. But do people create this content for free? What's the motivation for people to create great content for free on your forum?
How many people write authoritative blogs? Published a viral Youtube video? Contributed to Wikipedia?
It might be time for you to stop focusing on trying to get everyone to generate great content, and to focus on the very top group who generate the most content for your community.