I posted on a similar topic today. I'm seeing a lot of votes by brand new users who have less than 20SP and have not posted at all. I doubt they will earn anything. I don't think they understand how Steemit works and they may not even be reading posts.

I have over 400SP and only make about 1SP a week from curation. I mostly vote on posts that I read and enjoyed, especially those by people I know here, but I do the odd speculative vote on a post that I hope will earn something. It's not worth a lot of my time to do this if I'm only likely to earn a few SP cents. I'll vote up good comments on my posts too to show my appreciation. I know it won't actually earn them anything. It's just being social.