The purpose of Rep Points to help avoid the usual "post crap until I reach the minimum to access the good stuff" from happening. I know of other sites that use this method, and yer guaranteed to have 5-10 "crap" posts on random threads that let's be honest, are meaningless and detract from the effort the poster went to to post the article / pics. The fact that people come here to access the goodies and not contribute back is not what this community is about.
The Rep Points are supposed to show members appreciation for the time and effort you put into the site by posting articles and pics, and contributing to others posts. Those who have high rep points are generally considered "outstanding contributors", and the site would not be this good without them.
As for what the points can be used / traded for is a good question. Not sure if Chief has any thoughts on this topic, but the moment there are monetary based rewards for rep points, the back-door dealings of giving rep points for the sake of the rewards and not for the content will start. I guess you could trade the points for custom titles, avatars, etc. I've seen that work on other sites.