I think the correct thing to do is to reduce the proposal fee to zero, and ONLY IN THE CASE spam occurs, then rise the fee as much as it is required in order for the spam to stop. If the spam stops, then start again slowly reducing the fee until it reaches again zero, or until the spam starts again (in that case the fee will increase again). The rise or the fall of the proposal fee will be decided by a numerical voting among the masternodes (yes
vote the numbers once again)
The dynamicaly voted fee is the only correct thing to do. Anything else, and whatever hardcoded number is decided for the fee, it is just wrong and a waste of time (especially a waste of time for the people who are talking or complaining about it).
The developpers should respect the time of the people, and fix this problem once and forever.