There are a few places in the code that consider karma but IIRC it's never more than 500 (the downvote threshold). It's actually on my list to add more goodies for higher levels - maybe something like linkifying URLs in user profiles - but it would not have anything to do with authority on HN itself. We want the best comments and the best arguments to 'win', not skew things in insiders' favor.
Not sure what you mean about thresholds.
Yes, and I also do it, but very rarely and as an exception (and I am strongly in the position of "sniping weakens the system").
The issue is that it is possible that the censor may have misunderstood and missed something that was not clearly expressed.
I'd argue that in this case it's also in the interest of the community to downvote, since the comment adds more noise than it contributes to the discussion. In the end it's a ranking; if other comments are better worded and clearer, everything else being equal, they deserve to be higher up.
How would one know if flagging wasn't abused? I've had comments flagged that get unflagged a day later. Were there any consequences for the person who flagged the post?
Part of the issue is HN is too broad. Whatever goes here, really. Communities that work are focused on specific things.