PD3 is launching this term so it is important for us to sustain the full advertisement group. I do have plans to switch to a flat payment/pay per activity within 1-2 terms after I figure out pricing.
One thing that I could suggest would be to provide incentives to users to change their signature each day for the "10 days until PD3" signatures that you had posted on here ~a week ago.
Since you now have the ability to check everyone's signature you could check to see if everyone updated it and if so then credit them a certain bonus, maybe 0.005 BTC per day, starting at 10 days before PD3 is launched and maybe a .02 BTC bonus for users who change their signature everyday. You could potentially pay this ahead of schedule a few days after PD3 launches to give members an even bigger incentive to keep their signature updated.
For a way to cut down on the spam and increase the quality of posts, I would suggest something to the effect of maybe 75% of the maximum payout (as of now) in exchange for a minimum of 100 constructive posts for the month.
For example senior members can now make up to 0.48 BTC per month (.0012 * 400 posts = .48) so you could change to a flat payout of .36 (0.48 * 0.75 = 0.36 BTC) as long as the member posts
at least 100 posts. Going through the payment TX, it appears that the vast majority of members were paid for at least 100 posts. If you wanted to keep a 50 post minimum then you could use a 2nd tier of payouts for members who post between 50 and 99 posts for the month, maybe 66% of the new max payout for 100+ posts for the month.
Another option would be to pay per activity so that, on average a certain ranking member would receive the same amount for posting, say at least 100 posts for the month. The problem with this method is that, a full member with 120 activity for example would receive a larger pay cut while a full member with 239 activity would receive a less pay cut (or possibly an increase) and some may think this would be unfair.
These are just suggestions as to how to change the payout structure to increase post quality. While "eyeballing" the payout TX, it looks like that few members received the max payout, so I would think that these percentages would make it so few members would actually receive a pay cut.