Us humans are pretty simple creatures - motivated to seek pleasure and avoid pain.
I think this entire issue can be resolved by creating the right incentives. Incentives drive behavior. Ask any salesman (no offence to sales people) - They'll work the system to get the highest rewards.
It's human nature. So why try to get people to act in a right way - provide them the incentives to do so and they will naturally.
How to achieve this? Firstly, reduce the incentive for self-voting. If people don't get points for voting their own content - they likely wont. Improve incentives for those who interact with the platform more.
I realize this gets technical and just want to answer you at a high-level - which is simple work with human nature - not against it :)