In the last few weeks I have been to quite a few conferences around Alberta, and have been reflecting on the ideal conference size. A conference should involve information sharing and discussions or networking, the latter may be less possible at larger conferences.
Events like the annual ISTE Conference with about 20,000 attendees are impressive, and you may meet someone like Mayim Bialik, but it feels like the odds of meeting someone with whom you can have sustained and ongoing discussions are decreased. There is an ocean of information available, but I'd argue that through the internet we already have that available.
So perhaps the ideal conference size is between 150 and 500 participants. Large enough for a diversity of perspectives, but small enough to be able to meaningfully share those perspectives and get to know people. We tend to value growth as a measure of success, but perhaps we need other metrics.