Take my answer with a grain of salt as its clearly just my own experience and what I do.
That said, outside of friends I already know and go with, I really don't network or mingle with people at the conference much with exception to lunch time where you're sitting at the table talking to other attendees or staff. I pretty spend the majority of my time there in sessions and of course the keynotes.
So, as you said, the talks eventually get uploaded online so why go? In part because of the experience I guess, and in part, I go with friends so its a good way to meetup and hang out at the conference together. Swag is just icing.
