Maybe we should be thinking about this from a budgetary standpoint. If you want to reduce spammers, which will tend to be from new and low-activity accounts, than make posting cost go down as your reputation improves. Then set a decaying running-average posting price as a minimum posting rate for the best posters targeting a maximum site-cost per day or week. For example, you could have a three tier price structure based on reputation grade where low-grade reputation (new accounts) pays according to the present progressive pricing of posts, let's say it's set to ten cents as the base (500 sats adjusted monthly). In the second grade of trust, essentially community verified accounts, the base falls to 100 sats. Then the top tier (well trusted accounts) will pay 100 sats for the first post, 50 for the second new post, 25 the third, 13 the fourth, 7, 3, and 1 thereafter. The daily cost for the best posters would be well under 1000 sats which should be palatable to most anyone, particularly since a good poster will return his investment quickly with upvotes. The time since the last post will be factored according to the last posting time such that 24 hours will bring the rate back to the starting price. You may also consider charging more for posting and less for commenting such an 8:1 ratio.