But that doesn't work either. 20 plankton votes won't generate any reward.

Sure there are arbitrarily small votes which won't generate a reward, but if X is the amount necessary to generate a reward then two votes of 1/2 X will be sufficient, or ten votes of 1/10 X. That is the idea.

I see four comments with a payout and they all got one vote.

Sorry I misread one of them which I thought was multiple small votes adding up to a small payout of a few cents. I definitely have seen it on other posts, and the principle stands. Voting is for people to collaborate on payouts. If you want to be a lone wolf, send your own money as a tip.

The other 143 are worth almost nothing in comparison.

I don't know what sort of calculation you are making but within any single payout, vote weights are fully linear. Two votes with 1/2 X SP each are equal to one vote from an X SP (assuming equal mana/weight).

If there are people with more or less stake that is simply natural influence. More stake has more influence, as usual, but again within a single payout it is always linear (this was even true with n^2).

Tips never worked for because everybody is staking everything into Steem Power, not having any liquid STEEM to tip

Silly argument. There are around 100 million liquid STEEM in the system. I don't know the exact fraction of active accounts with some liquid STEEM or SBD but I would estimate it to be very high.

There certainly might be reasons people don't want to tip but that isn't a big one.

A sub linear reward curve would have the potential the change that because you reach the point where staking more won't make sense.

As I stated before, a sub-linear curve will not work. There will never be a sublinear curve, probably not only on Steem but on any similar system (which doesn't rapidly collapse).

Nice idea in theory. In practice it is a non-starter.