Numbers do matter for conferences but they are not the only factor in their success - I think venue and event/activity design also matter. The actKM conference was a very happy combination of a wonderful venue with natural light (in which I think you had a hand), the numbers diversity and the attitudes of participants, and a variety of activities, not just passive listening.

If we extend this to KM in general it suggests that it's worth keeping an eye on numbers, but also working on the other "human friendly" factors.