I think this is an excellent idea. I don't know if I fully agree with this bulletpoint though:

Bots are negatively affected: automatically voting for "sure things" is not a good strategy anymore.

I agree that bots are adversely affected, but disagree that "sure thing voting" is no longer a good strategy.

While it's true users wouldn't be able to place repeated full-power votes for the same person; I think they would continue to upvote these sure thing posts (just at a forced lower percentage) because they aren't punished for voting for the same users repeatedly.

Bots and humans alike would be forced to use this "extra" voting power on other posts. Thus achieving the desired effect of having more authors getting discovered and a wider variety of posts getting attention.

I am not advocating punishing people for voting for the same authors repeatedly. I like your idea the way it is.