The problem is that the rep system usually gets misused. Trolls gather together and keep repping eachother and give solid posters negative rep, just to troll. Not only trolls, but friends usually give eachother rep as well. In the end it becomes more of a popularity contest.
Personally, I think head-fi should scrap the headphonus supremus tags and stop showing post count and join date at all. The forums I've been to where they have decided against showing post counts have actually become better from it. People get less prone to the authoritarian way of communicating that way.
First paragraph: I don't yet know how it works on this forum, but what you described (or versions of it) certainly exist--even on "adult only" forums.
Second paragraph: More accurate information is never worse than less accurate information. If you find it to be irrelevant, just use your personal filter and ignore it. I'll add that some of the most polite posters are in the upper levels of this forum.