Might I suggest also looking at Proposal to fix governance proposal rewards at 75% on a daily basis
I’m curious how you and @lara might judge this proposal on each of the criteria you’ve described, in terms of its goal to limit the financial incentive behind submitting spam proposals.
I think fixing governance proposal rewards would specifically work very well in tandem with the “Voting in stages” proposal suggested by @lastmjs, especially since that proposal solves the advertisement/visibility incentives behind spam proposals, but does not solve the financial incentives.