Not sure of my opinion on post count, but I still think it's a largely useless factoid. I personally see usergroups and don't really think differently about those with a higher (or lower, although that's not possible) rank. It does nothing to tell me anything about the quality of their posts.
As for rep systems, at least here I think it would either be abused by people who vote just for popularity or by people who just rep well-known users. I'm trying to look at this from an objective standpoint and I don't really see an upside to its implementation here personally. Sure, you can mod abuse, but if basically every single rep given out is out of popularity, I don't see why it should even be implemented.
I may have a history of being at odds with the staff's opinion, but I'm just sharing my personal thoughts here and I'm trying my best to remove any subjective biases I may have.
I'm not really sure of what to suggest here though, other than looking over a user's posts to determine if they're a helpful poster or not. The reason this is different from looking at a rep is that rep is a combination of subjective opinions and a mini popularity contest. All it would say to me is "a lot of people like what this guy says, but that doesn't necessarily mean his posts are quality or helpful simply from his high rep". In the end, to best determine a poster's helpfulness, the most accurate method for every individual to tell is to look over the posts. I'm not really sure how you would implement that as a system.
I probably haven't said much of anything constructive, so I'll quit rambling, but rep is the system I feel most ill at ease with personally.