Jamie,
I am going to be a new mom... so as of right now I am far away from the PTA meetings. I do however think that it could be that people just don't know what PTA is all about.
My mother was super involved which helped me keep up with events in the school and really opened up some fabulous opportunities for myself.
I know that the mother's that really get involved will not be doing it for personal gratification, but to help make a difference in their child's learning environment.
I think if stay focused on trying to get Mom;s involved that will participate simply b/c they think they can make a difference for the children in that area, you may have few numbers but good people with you. I would rather have 5 members that are anxious to be creative and proactive than parents that just want to be there to say ... "yeah i'm in the PTA"
But to get off my rant and really answer your question...
A funfair that not only would help raise money but give you an chance to do something fun for the school but also get the parents together to talk with them about the benefits of being a PTA parent and how helpful it is for the school. I am not saying tilt a whirl or anything. But some kind of BBQ-ish event with games like potato sack relays, egg toss, pie in the face, bean bag toss... Stuff like that. Where you dont spend much money so the entry fee is cheap and won't scare any potential members off!