The problem is again: either all vests are equal or they are not. There are not many safe ways to counter this "self voting". You can always delegate power to another account. It can never be detected. Period.
The only thing you can do with respect to self voting is flagging. Although a flag is only warranted in the same case as before - when a post is making more than it is worth. If someone self-votes their post to 50 cents, and that post goes on to make 10 dollars, there was clearly not a problem with the self vote.
The fall to Nash is futile.
I'm doing work with the steem blockchain API, although haven't been for long. Surely SP delegation operations are traceable in the blockchain? I must admit I haven't actually seen any yet, but I haven't been looking.
They are iirc.
That does not stop someone from having anonymous accounts do their work. Delegation smart contracts could provide this as a service. There is always a way to self vote with vests you own. - unless not all vests are worth the same.
There is no way to detect or prevent self votes. Period.