Im not sure we can have "good quality speech (Signal)" without some degree of "bad quality speech (noise)". Arguably one man's trash is another man's treasure too.
One challenge is it may well become like x / twitters "freedom of speech, not reach" policy if it went the financial route.
Which I'm not sure if this is the best overall outcome for all either, even if there are benefits.
Would a better strategy be to allow functionality for folk to amplify and attenuate signal / noise in some way i.e. via
Communities / Groups?
Those good at picking up Signal might help others find it also. Perhaps with a small entry fee or credibility qualification into a Community.
Sorry - I feel like I'm offering more problems than solutions. Something like this probably requires a fair degree of prudence. Though I like what you are driving at in many ways.
Some degree of bad actors has to be allowed I think for it to flourish. The OG Bitcoiners / Cypherpunks were arguably 'bad actors' once upon a time.