I think getting no downvotes for an extended period should be recognised, for example:
- no downvotes for 25 consecutive answers: bronze
- no downvotes for 80 consecutive answers: silver
- no downvotes for 200 consecutive answers: gold
It would be a mark of quality of answers, rather than sheer quantity, which is how some make reputation.
Perhaps to stop a driveby downvote affecting the clean run, it could be "less than 1% of votes are down votes" or similar