There's obvious value in meeting people connected with, and hearing experts speak on, a theme of interest to you. I've been to a couple of residential conferences in the last ten years: last year's cataloguing conference at Exeter, which I mentioned here, and a few years ago the CILIP rare books group conference. In my experience each such event results in at least one change of practice at work or useful future contact. In earlier jobs I have been to various area studies events (often cliquey!), and CILIP Cymru and UC &R group events. If you are shy, as I am, the world of business cards and networking doesn't come easily, and I am quite sure I have missed opportunities to talk to the right people.
Speaking at conferences
NOOO! I'm not at all comfortable with public speaking although I feel I should be. I come from a family of teachers and clergy, after all! I suspect that this is something which simply comes more easily with practice, although you can usually tell that even quite experienced speakers are nervous. I'm not keen on death-by-Powerpoint, although Powerpoint really should make public speaking easier for those lacking confidence, as it diverts attention from speaker to screen. I'm not sure I could handle Prezi well either. I have contributed to internal days for staff at work, on both occasions sharing the stage with colleagues who had done the lion's share of the preparation.
I had one job which included event organisation to a certain extent, but it's a long time since I've done anything like it, and it certainly did not involve anything as big as a conference. In that particular job there was a well-organised infrastructure in terms of catering arrangements and rooms: the practical aspects of event planning can be quite a headache without this behind you.
I'm always surprised at how many parents of children still seem to be able to take part in events, especially ones involving overnight stays away from home. I have as I say managed it a couple of times, but it involved a lot of planning: I can rarely go to anything outside school hours without my husband taking time off, and as he doen't get as much leave as I do this is not often practicable. This is as much a problem before 9 a.m. as it is in the late afternoon and the evening, so it is difficult to travel very far during the day either. Thank goodness for Twitter and its hashtags for helping the stay-at-homes to stay in touch!