A "hello" board would serve a few purposes:
1) As stated, it gets all "hello" threads into one forum.
2) If we had one from the get go, it would easily rank at least in the middle of the pack (of all boards) in terms of activity. In other words, it will get used a significant amount.
3) It *invites* members to introduce themselves. This gives them an opportunity to establish their interests and objectives. If they provide implicit questions ("I want to be able to do blah blah blah"), someone can give them some pointers. If they join and establish they have a certain skill, they can be immediately recruited for one of our projects. If nothing else, it helps break the ice, which should increase the activity on our boards a bit (can't really say how much, though).
Besides, what harm is there in having a 24th public board when you already have 23?