I think that Aurora's got a lock on a big part of the problem. You can offer to open up older fiction to younger generations but that doesn't mean they will like it. Short attention spans and more popular fiction means less chance that they'll like what they read. If it isn't Harry Potter or Percy Jackson or Hunger Games....
If the folks in charge of programming don't ask the younger contingent what they're interested in seeing or hearing about, then the programming will contain stuff the younger contingent isn't interested in hearing about, and they're not going to spend the money they have going to events that don't appeal to their tastes.
Another point: if all the programming casts in the direction of a single track to the exclusion of other interests, then the folks who might be interested in doing other things don't get what they want either, and it becomes darn hard to justify the expense.
Membership cost is just part of the overall picture, by the way. When you lump in the cost of a membership (possibly times two, three or more in the case of a family), then add in a hotel room at $100 or more per night, plus transportation and food, and suddenly the weekend goes from affordable to the only vacation a family gets in a year. Add to that the iffy status of programming (whether there will be enough to draw the crowd you intend to attract) and it suddenly becomes impossible for first or second generation fandom to bring along the next generation.
Take my case as an example: I think it's highly likely I won't make it to another WorldCon and increasingly likely I won't make it to any more local cons either, because by the time I factor in three memberships and the rest on top of my meager salary, it's just not possible. I want to come to Costume-Con next year, but financially and timing-wise, I don't see how I can manage it.
I attended Balticon this year because I worked as many panels as I could manage, saw next to nothing and couldn't afford much in the dealer room. All my free money went toward food and room expenses and that was without the girls in tow. On top of that, when I looked at the movie list, there wasn't anything I wanted to see. Panels I'd have been interested in attending were up against the ones I was on, and there just weren't that many. Roaming the dealer room without available funds was akin to torture. And I'm not yet 50. A bunch of my friends are older and hitting retirement or disability fixed incomes (or both).
If you're still single and under 30, your interests are going to be different from a fan who's pushing 50 with a family in tow. Finding a balance between the two means hard work and understanding the market, not just getting the same group of friends together year after year to go over the same material without regard to the rest of the audience.
I work in a theatre that caters to an older generation with items that occasionally attract a younger audience. We aren't committed to producing just for one audience but that has made it hard for us to build a consistent following because what appeals to some of our audience doesn't appeal to another part. So we get one or two-time visitors, or people who see only one or two productions a year. (It's part of why I only work part-time, but convincing the powers that be that they're doing it wrong has proved insurmountable.)
So what do you do? I'd suggest recruiting department heads nearer to the younger generation if you want to appeal to the younger generation. Or find people who understand and are comfortable with reaching out to multiple sources for program inspiration. Without the crossover, eventually the event will die.
My $0.02, adjusted for inflation. Your mileage may vary.