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).

You're talking about the 50 rshares reduction?

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.

Is there a store of empty accounts somewhere someone is willing to sell in bulk at a large discount? Sure, the 3 STEEM (not SP) is just a start up cost.

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.

Of course, I'm not talking about those votes that are given at or very near zero.

You should take a look at the user @eforucom. I've been following his rewards on SteemWorld. Maybe you have tools ready at hand that allow you to look at this user's curation rewards and voting behavior from a longer time period. While his curation rewards haven't been anything to write home about very recently, I recall seeing weeks when his curation efficiency was greater than 150% prior to HF 21. Lot's of relatively small automated upvotes. Nowhere near the vote dust threshold, obviously, but quite small anyway. A lot of the curation taking place here is automated. That's not too bad if the authors are picked with some care.

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.

I think automated and thoughtless curation, which was one of the issues raised here is not "mostly wrong". That includes things like front running bid botted crap content.