I think the points for posting are a good for the "PO economy". Maybe to help clean it up you add a feature to be able to +1 or like individual comments or threads. If a comment gets 5 +1s or likes THEN the person gets the points. That way you are only rewarding the posts that are adding value to the forums.

I know it's a separate issue, but rrickir has a really good point about people being really bad about paying back loans. One of the biggest problems I've noticed is that alot of previously active members had credit card reversals and went into some seriously negative points so they decided it wasn't worth it and left PO. Maybe you could reach out to them and offer to a 50/50 deal where half any new points earned would pay down the debt and half they could continue to use for whatever.

One last thought, I know the forums need some cleaning up, but based on azraels comments, he thinks almost everything is spam!! I'm curious to see how that actually works out...