I don't think new users should worry too much about curation rewards. By all means vote on what you like, but don't expect much. Concentrate on making good posts to build a following. I still make 10x as much from author rewards as from curation. You can even earn well from good comments.

But when you do vote seek out the good posts that are not getting attention to encourage those authors. As you say, it's not worth voting on posts that are already trending. Those authors are generally doing okay anyway.