I virtually 100% agree with you here!
The figure I basically had in mind was 25% (or 2.5) per day. Obviously free downvotes have their downsides (toxicity, abuse etc) but they need to be enough to threaten the status quo. I feel that anything between 1.5-3.5 might be a reasonable guess.
So as a self voter and a conspicuous one at that, i'd expect that my farm posts would be nuked to oblivion when these changes are implemented by free downvotes. Good. I, and others like me, will get the message loud and clear and would likely not bother continuing farming, especially when curation is paying a decent amount (say 50%). We will likely not like the fact that others (self voters, vote sellers) get to benefit while we don't. So we'll use our free downvotes to take others down, and paid posts will be pretty high on that list.
The idea is to migrate profitable voting behavior from content indfferent to content reflective behavior. Imagine if the bid bots are now competing as curation services - it'll mean we'll no longer have a proof of brain dead blockchain.
I am not sure if this solves the problem of bidbots and self-voting. It will be very hard to bring down a 200$ trending post when it is voted up 13 hours before payout, leaving you with just 1hour to downvote it...
I think bidbots will come up with some autovote function. Pay now, get voted 13 hours before payout...
Maybe (I am very skeptic about it) it is worth a try if nobody figures out something better. But I want a scheduled automatic revoke of these changes UNLESS the community votes to keep it.