Unless you are using a forum purely as an information source, getting involved is always more rewarding. As far as collaborations go, writing lyrics for someone else's music I can do ... I'll see how things work with my own stuff before diving into that. Getting into the forums and commenting on other people's work won't be a problem.
I think it's a case of jump in and see what happens. At the worst it'll mean I'll hear a lot of new tunes, learn a lot about other peoples approaches to writing and see what I come up with under 'pressure' to produce.
Sounds like a fun challenge , succeed or fail!