I just gave a few downvotes, it felt good. I do not have a lot of Steem Power though. Yesterday I made a post and got a downvote because I used some DEC to buy a vote from SteemMonsters, at the end of the day the downvote didn't affect me a lot but I learned my lesson. And you are right, a post promotion should not have a revenue or ROI.
And I think that the downvote attracted other votes of users with good power in Tokens, someone with 250k Neoxian gave me a 20% vote, so I'm not that mad ;). I will not buy votes that big anymore and I will make better posts.