One possible conclusion you haven`t canvassed, Percy, (AFAICR) in your determination to attract a better class of creationist, is that they have lurked here for a while, shook their heads at the very tolerance shown to loons, and moved on.
If any poster has to run the gauntlet of deluded individuals who spout whatever nonsense erupts in their minds sans reason or at least the semblance of ordered thinking, I can understand their reluctance to lay out their world-view.
Then, we have a repetition of the same dumb-ass, straw-man posturings as peddled by the mainline Creo sites and hardly ever get a new approach, a new challenge to the EvC board.
Some (including yourself) have tried the Devil`s Advocate stance, but usually run out of puff after the position gets increasingly ridiculous.
It`s probably anti-democratic, but I think we might have to set up a two-tier, invitation only, system, whereby selected members can discuss at depth and at length, without the interruptions from the loon squad. Showcase has no real standards, one-on-one in the Great Debate is too limiting, possibly an award to enter the upper forum decided by a vote of members might work. Otherwise, you will have to be the judge of who brings quality debate to the Upper House/Senate. This might work better than the POTM nomination.