the motive behind the inspiration was not promoting the actions of Lego but the key idea that building things with an element of fun an play helps ignite hidden creativity and develop it also. At the Art Centre College,California a lot of these fun building blocks like toys and construction sets are used to explore forms and mechanisms helping people in the age group of 18-30 express their creativity.
I would like to view these events as seasonal episodes of the same project thus each event involving its share of unique activities & discussions, and leaving an incomplete but surprising end that leaves people to think. There could be parades, collective reading and sharing of people's stories, community events, plays/acts performed, special offers in certain partner food joints where every one could meet and acknowledge the day.
Nathan I really like your idea and I wish we can find a way to keep up the spirit of the day with each passing year because most of these days just loose the rhythm mid way. We should work out activities that leave a strong effect on people that lasts till the next Intergenerational Health Holiday arrives.