The best incentives are non monetary. Real people are motivated by them.
To get that you'd need to spend like 6-7 months on HN submitting quality stuff or making quality posts(need those votes). Noone is going to do all that for a single link, they'd rather spend that time adding their site to a bunch of directories or writing articles to submit to content farms.
Votingrings with sockpuppets would be detected long before they would get even near that level, presumably long before they'd reach even 10% of what it takes to get on the leaderboard.
There must be softer targets than the HN leaderboard.
front page: PR7 page 2: PR0
the top100 leaderboard user profile on the other hand: PR4
There are a lot of guys here working hard on their startups who have also spent a boatload of hours on HN submitting, ranking, and commenting. Giving them a little GoogleJuice doesn't hurt HN at all (want to take a year to get on the board just for one link? Don't think so) and it helps some of us out a bit.
The term "Leader" makes me uncomfortable in the first place, English is not my first language, that's why maybe it resonate for me as in : "The persons who rules the others".
In my opinion "Top contributors" would be more appropriate.
"Leader" can imply "ruler," but it can also mean someone who is winning a competition (his opponent are behind in score and hence are "following" him) or someone whom other voluntarily follow.
It is generally considered a benign term.