A few months ago we ran ads for Dragonmirth submissions because we wanted to see it come back.
We received about 6 submissions over the course of about 4 months.
I'm going to be blunt here and suggest that the wording of your request was less-than-ideal. It essentially stated (and if this was not the intent, then it was a poorly-written blurb) that entries to Dragonmirth would not be paid for their successful submissions. In other words, that the "exposure" of being in Dragon Magazine was the primary compensation. As a freelance artist, I can tell you that doing work for the sake of exposure is generally considered a sucker's game. The exposure never really amounts to anything, and you're out a piece of work someone else might have paid you for. Further, the blurb suggested that you MIGHT get paid, IF you did regular pieces that were accepted over a period of time. That sounds even worse, because it implies that Dragon could potentially string a cartoonist along for months before paying him—or even stop running his work after getting 5 or 6 free comics out of him. The whole paragraph read like Dragon was trying to milk something for nothing out of its readers.
I would have strongly considered submitting Dragonmirth cartoons—a number of my regular readers actually begged me to—but the request sounded fishy. I have no doubt that this significantly depressed the number of submissions.