Why add a blog? Why not just use the forum to post in depth write-ups? For example Brett's "26 steps to 15k a day" was a blog quality post but was published via forum.
I guess some blog platforms might handle trackbacks and pings better than some forum platforms but I don't think the answer lies within publishing methods.
I think the key is as netmeg mentions "have something worthwhile to say". if you don't have enough to say or enough time to write it up then consider recruiting forum members that will commit to posting a long, blog quality post once a week. That way the workload is spread out and isn't a burden on any one person.