OK the way it works is like this: if you upvote within the first 30 minutes, you are giving most of your curation award to the author. If you upvote after 30 minutes, you keep the curation award.
When you are upvoting a post that already has a lot of rewards, you frequently see a rise in the $$, but this is because your vote is added to a lot of other people's votes, and sometimes you "tip" the rshares enough to increase the total reward. However, it is unlikely that you will get a curation award for your efforts, especially if you have voted after a whale.
If that all sounds very confusing, you might like to look at the detail of your posts in steemd.
Here is the steemd version of this article:
Click "advanced mode" and then scroll down and click "vote details".
You should see a list of everyone who has voted. The total of the rshares determines the total reward for the post. The total reward is split 75% to the author and 25% to the curators. The "wgt %" is the percentage each voter gets of the curation award.
RE: At what point (in steem power) does an up vote have a financial effect