I guess the motivational effect of the leaderboard is biggest for people near its cutoff. I guess that increasing the number of leaderboard slots means a small overall motivation increase (good, I guess), and a shift of motivation from higher up to lower down (not so good, I guess).
The other point of the leaderboard is to help readers get a sense of who's who. A longer leaderboard contains more information, but I suspect is less digestible.
None of this seems like an obvious win (nor a big loss).
I'm wondering what the optimal number of people on the leaderboard would be. I suspect that people who appear on the leaderboard post more often because they want to remain on it. The other advantage, is that if the leaderboard seems in reach, more people will compete to get on it.On the other hand, if too many people were added to the leaderboard, then "being on the leaderboard" would be worthless and people would only care if they had a high position.
There are currently 15 people on the leaderboard. I suspect that if there were 20 people on the leaderboard, that would increase the motivation effect, without significantly devaluing being on the leaderboard itself.
What do people think?