I think upvotes are for the quality of the content in the post and comments are for sharing your opinion.
So, upvote when the post fits the purpose of the community, spurs discussion, and follows the rules.
Comment to tell people what you think about the content of the post.
If we downvoted every time there was horrible news we didn't agree with communities like news and politics would never receive a single upvote.
Do it! I made the plunge and have zero regrets. Everything works, it's fun, and I get to annoyingly pester friends, family, and strangers about the benefits of open source software!