I upvote things that I find worthwhile and that is how I thought it worked as well.
But I just did a search and found out that you get paid for casting a vote. As long as you cast your vote within 30 mins of the post being new. The amount that you earn would also increase as time gets closer to the 30 min limit.
Below post from: https://steemit.com/steem/@steemship/how-to-vote-smart-and-profit-from-steemit-s-new-curation-rewards
“Starting *TODAY all curation rewards earned by voting in the first 30 minutes after a post is made will be shared with the author. If you vote immediately after a post is made, then 99.94% of the curation reward will go to the author. If you vote after 15 minutes, then 50% will go to the author. Any votes made 30 minutes or later 100% will go to the curator. This only applies to the curation rewards. The author still gets at least 50% of the total rewards.”