I think this is a good observation. Events seem like something you could unbundle from Facebook into it's own social media app.
Part of the problem with a standalone event app is that you don't get the network effects of normal social networks or the daily usage.
One interesting route might be to make an entire social media app / platform around this. Not with the meeting up itself being the core component, but that "event" concept from Facebook.
I have an event coming up this weekend that I'm tracking on Facebook and would have probably forgot about otherwise. There has been a lot going on in there leading up to the event. Conversations around reservations, parking, plans, well wishes of people who can't make it.
Each event (again the software component not the meatspace counterpart) acts as it's own self contained social network almost.
One interesting thing I've actually considered before about events on Facebook is that all the best content for the event usually doesn't go in there. The pictures and discussions for after. The inside jokes and so on. With facebooks design there isn't really a good reason to go back to the event after it has passed.
If you built an app around that you might be able to approach it differently.
Just some rambling thoughts. Cool idea - good luck!
