I am with @steevc. I think the far better ROI will be achieved by a rise in STEEM-price. So acting in a way that favors the growth seems to be the better strategy in the long run.
Yes, it probably will not make a big difference if I self-vote instead of voting others. But if everybody thinks that way, it will make a HUGE difference.
And yes, I would make a few times more money by just self upvoting a lot more. And yes, I have thought about it too, I don't want to lie.
But as long as I find enough valuable content (it doesn't have to be about topics I like, it just has to be content which I think is beneficial to the growth!) to upvote, I think I will go that way ;)
And that strategy would be n^2.
Under n^2 the rewards for my posts would shrink a lot.
I would probably not earn much from posting anymore.
My Steem had at least the chance to become really valuable then, though.