This already exists. Every vote has a dust vote reduction in order to discourage vote spam. Very small votes are worth less and earn less. A small to moderate stakeholder who splits into 10000 0.1% votes per day will give up a lot of their vote power, possibly all of it (on this note, also see third paragraph).

Account splitting is another issue, and no the 3 SP isn't a major obstacle because: a) empty accounts can be bought in bulk, and b) if the strategy is significantly profitable then the 3 SP is just a start up cost which would eventually be recouped anyway.

Also, many of the dust votes you see are in fact pointless. They're made at zero seconds which means they forfeit any curation rewards even if they earned any. I believe you have inferred some sort of intelligence or strategy behind them when none exists. I don't know why people are doing that, other than ignorance about how the platform works perhaps.

BTW, I added a tiny upvote to your post even though the idea is mostly if not entirely wrong, because it is good to examine such things and raise questions.