I may have already mentioned this (apologies, lot of comment threads going on), but what do you think about tying voting power more to reputation as @valued-customer suggests?
If reputation was more important, that could become an additional curation reward (Whether it be the standard rep or a second curation rep) without tapping the reward pool.
If the curve isn't too harsh, that may not be much of a disincentive from users buying in. I doubt many new Steemit users (a lot of which aren't totally crypto-savvy) are buying in their first week, and it doesn't take long to get to at least the 30s-50s.
I think if the standard reputation couldn't be affected by self-voting, then that might be a good idea, but unfortunately I think many existing reps have now been distorted by the self-voting problem itself.
It may not be popular, but actually if in the next hard-fork, the reputations were recalculated not to include self-voting, this may help. Of course though, it wouldn't do anything to solve the problems where reps had been artificially elevated though vote trading and sock puppets.
An additional curation rep is an interesting idea that I'd need to think about more, but it sounds intuitively like it might be good. It does have the disadvantage making thing seem more complex for the user, although I guess it could be hidden from the interface.
Indeed, I was thinking of curation rep as being hidden from the interface.
If the curve for curation was changed so that the more of it you did, the more rewarding it was over long periods of time, perhaps that would help too. Similar end achieved as adding a curation reputation.