At 20k, you should downvote and vote to delete. Flags for moderator attention should be reserved for posts that you cannot handle yourself or require immediate attention. We want the community to be involved in moderation. From A Theory of Moderation (emphasis original):
[W]hat do community moderators do? The short answer is, as little as possible!
This is for the same reason we want 3k users to vote to close rather than flag when possible. See How should my flagging change when I gain the ability to vote to close?