If you take away the ability for abusive self-voting to give significant rewards without a pile-on of other voters, then you are also taking away the "regular users" ability to influence rewards.
Bingo. This smacks of a fundamental tradeoff, or a conservation-of-crappiness law. "Conservation of unfairness?" That would be a fantastic title for a paper. The law, in laymen's terms, would go something like "all systems are at least somewhat unfair; you just have to decide where to put the unfairness."