Self voting is not a problem, selfish voting is. Votes which are at the expense of community engagement and satisfaction, such as auto votes and circle jerk votes that result in the same users getting to the trending page every day. Those things cause disengagement and do not even benefit the short sighted selfish voter.

As for a code solution, I suggest incentives to seek out new users, by varying the ratio of curation rewards to post rewards according to how many followers a user has and how many vests those followers have.

https://steemit.com/curation/@beanz/the-problem-with-the-current-curation-system

Yes, there are ways this can be gamed, however I don't see the results of this to be bad for the community.

It would reduce the benefits of current system of automated voting if curation rewards for popular authors were lower, and whales could also prevent "pile ons" for curation rewards by using their SP to follow authors that are being voted for out of speculation of the curation payout.

Whales and dolphins would be incentivised to seek out new users for higher curation rewards, giving all new steemians a welcome and proper chance of achieving recognition.