Someone looking to mine the reward pool would simply create many small accounts to vote on to get around this restriction.

True, but are you satisfied with that state of affairs? is there anybody looking at how to break that symmetry? The "upvote" is not an exchange as would occur in real life, although there are two parties, it is not a trade - because the reverse "upvote" has the same effect.

There must be a function (somewhere) that can act as an asymmetry to the upvote function.

Any "vote decreasing" function will have a nuisance-effect on many but, as you say, will ultimately lead to more complex self-voting structures.

BTW thanks for the article and thanks for answering some valid technical questions in the same tech fashion.