I really like the idea of this sub-board. Only the actual educated discussions can get through, it's good. The problem is, it goes on huge periods of not being used ever, meanwhile I imagine a lot of people send in Gameplay+ posts that either don't get looked at or get rejected. One thing you can do is potentially being less strict. I'm not sure about what guidelines the moderators use to accept Gameplay+ posts, but with so few being accepted, maybe these guidelines are a bit too strict. I understand this is supposed to be heavily moderated but what's the point of having good discussion if there's almost no discussion at all?
I think the goal should be to get (on average) about 1 thread on there every other day. Now you may not get the amount of requests needed for this, and to that I say maybe just get it out there more? I'm not sure exactly how to do this, but if more people know about it more people would want to post there.
Obviously my suggestions aren't the best ones, but I just hate seeing this sub-board being semi-dead so I just decided to throw some things out there. Feel free to flame my ideas if you want.