I think the content and the community are enough incentive. Problem is it takes time to realize it. At first glance Hubski is just a bunch of links, it's hard to realize the people behind those links and comments without investing some time. I know mk is working on a way to showcase the people (you all) that is more overt. It may help in your cause. Keep spreading the word! I love seeing Hubski links in the wild.
When I tell people that I co-founded and have been working on Hubski for 5 years, they immediately ask if we make money. When I tell them it actually costs is money they think we are insane. Making music also costs me money. Many things that are worth while do not have a profit motive ascribed to it. Building something of worth is enough reward. You would be hard pressed to find many other communities where the intent wasn't to grow, grow, grow. I'd like more people, but only because I know there are people out there searching for something like Hubski. Plus we all benefit from more, interesting people. But I have no illusions that Hubski will make me monetarily wealthy. It's certainly enriched me though.