For the curious, I put in the initial minnowbooster shortly after this post. I paid 2.95 SBD for a $5.72 upvote. Assuming I get the full amount of that vote, the return at a SBD price of 5.36 USD is

1/2 * 5.72 * (1 + 1/5.36) - 2.95 ~ 0.44

or a return of 14.9% of the initial payment. This can get pretty ridiculous if using much higher amounts too.