In principle, our forum topics are well indexed. Right now, Google has indexed 5600 edgeryders.eu topics. Not sure when and how it will happen to any new topic, though.
And Google also provides us with quite some organic traffic – it’s not like it considers a forum “low quality” just because it’s a forum. So I think if you want to go for more organic traffic, it’s about finding out what people are searching for, and writing unique content for that.
We did not really shoot for that so far but had some accidental success with some forum topics … the egderyders.eu topic with the most external traffic is, strange enough, “List: Open source software for resource scheduling and booking” (17,200 clicks until now).