I think you're going to need the equivalent of a Marketing Campaign, complete with Loss Leaders (which you yourself did with cheapy first-timer memberships at Continuum) and a very proactive recruiting campaign. I think that Fancons, and Fandom in general, really have to be "Sold" to the neofans, if you're going to get their interest.

Something I never managed to get going when I was MSFC President, but which I think is an idea with merit, was an Outreach team, which I envisaged as proactively visiting various different meetings, groups and organisations, getting involved with them on their turf, and generally spreading the word. I don't know how adaptable that idea might be to the Conventioneering side of things, however.