In the grand scheme of things, the user base of HN is relatively small. Now, divide that into a much smaller number and that's the potential user base for your site. My point with this is that targeting only HN users for something like this will result in what you're seeing - not much attention.
I say this because HN (and online forums, message boards, etc, in general), in my opinion, helps to solve a problem that existed prior to its existence. That problem being that there are a lot of people with the knowledge and ability to help each other with tech and business, but they're all spread out so it's difficult to meet in person. Message boards like Stack Overflow, Quora and HN help bridge that separation. Your site, on the other hand, is attempting to tackle that issue head on by providing a way to help people setup in person meetups, except that you have an added difficulty in the fact that you're pitching it to a crowd of people using a service that allowed them to come together because they're all spread apart in the first place! (whew)
Now, obviously your idea works elsewhere - meetup.com. They're focusing on a much broader target market, though. Perhaps for your idea to work you could include ways to help HNers make it possible to meet up in person? Perhaps locate cheap plane ticket pricing, or groupon-esque deals for restaurants and let them make reservations. Those are just some less informal ideas, but I think something along those lines might be helpful to your service.