I have a system where you earn based on the number of characters in the post. You only get 1 point for the post but make 2 points per character after you hit 5 characters in the post. If you start a thread you get 10 points for replies to that thread. Once they get the requirements for the package they want they just go to the forum where they request it which has permissions set so they cannot get to it without the requirements met. I use MyBB and newpoints for this. It does update the points during edits and I think it does if deleted. Also, if they refer someone to the forum they get points too. You can set some forums to pay more or less if you want too.
For example, this post is worth 1664 points with my system. I just set the point requirement really high.
It would only take 12 of this post to get 20,000 points.