Although I am usually 100% opposed to anything that smacks of "pay to publish" I think maybe MPP should be limited to PAYING members. Without real editorial gatekeepers, $5/mo seems like a "put your money where your mouth is" gamble - and if you cannot earn it back consistently after a month or two of learning the ropes, then maybe, just maybe, your work - or your collaborative spirit, your willingness to support and promote others and this site - doesn't merit it.
IF I were Ev (and clearly I'm not), I think I'd make MPP open ONLY to paying members, and still let anyone who wants to publish their stories here. I'm not sure that would work, either. But the trick is to hang in and keep trying till you hit that sweet spot, where the best work gets paid for and you can bring in enough paying members to support that.