The existing non-linearity already gives an incentive to curators to vote on posts that other people will also likely vote on rather than simply self-voting.
The reason this doesn't work well in practice is at least in part to the fact that most of the rewards go to the author rather than the curators under the current rules.
The other problem is few people understand the real rules which are essentially undocumented and end up fighting shadows.
I'm open to any solutions that resolve the current situation. I'm interested to hear more on this type of solution involving the current % allocated to curators.
Pay more for curators than authors and people will vote for others instead.