The highest ROI even for smaller accounts is to find unknown content that figures to be successful once it becomes visible and vote on it. You won't earn as much as a larger account in absolute terms, but you may actually earn more relative to your SP level (return on investment).
Voting mechanically for authors with the best track record doesn't work to generate the highest return because you have to vote earlier and earlier to get ahead of everyone else doing the same thing, which then reduces the curation rewards (the system docks them back to the reward pool for votes before 15 minutes).