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are upvotes on posts more than 30 minutes old worthless to both author and curator?

Regarding the author - Not at all worthless. Every upvote adds to the payout for the author.

For the curator - Depending on how many people voted before you and how many people vote after you, you could receive a small or a large curation reward.

Aah! Brilliant, thanks for clarifying.

And again, great post.

You're welcome. And thank you.