So I think that you're looking at Steemit as a purely investment strategy as opposed to a social media platform. I'm looking at it from the Social Media perspective. Rewards are ancillary. Therefore, blocktrades not using all of his votes on a daily basis does not negatively impact the quality of content provided on the platform. On the contrary, bot votes for poor quality content does negatively impact the platform.
Now, the rewards are definitely a draw for any new user. Other users will like the idea that this is all based on a blockchain (others will never adopt for the same reason-something about my writing lasting for eternity is partially harrowing).
I don't think that whales need to be 100% active on the platform in order for it to be successful as the platform grows. There will be plenty of medium size fish who keep everyone afloat (think middle class in an economy). The uber rich do very little, the upper middle class does the most (trying to become uber rich), the rest of the middle class does what they can, and the poor are trying to climb up the ladder.
I think that in a mature Steemit economy, we will see something like that. And if a whale wants to augment their income on the platform again, all they have to do is put in some manual effort themselves (or to a delegate).