Many people hold cherished childhood memories of lego sets that they remember from their youth. They have gone on to share this enthusiasm with their children and their children's children and warmly remember their own favourites. The sets have become iconic and, as such, deserve preservation and celebration for generations to come.
Lego sets are a grand mix of engineering and artistic expression. Museums around the world house the works of art from the ages and today. Lego sets are a part of that. The only added bonus is that Lego sets allow the masses to not only enjoy the art, they can build it from the ground up, too! Lego sets deserve to be preserved.
I think it is interesting to preserve all Lego sets every made as historical artifacts. I don't know that they need to be guarded in a secret underground facility, but I think they have a place in a museum for American toys and culture. Toys from different time periods provide historical evidence as to people's leisure activities in their time.
There are countless artifacts in museums today that have questionable cultural significance. We find significance in these meaningless items because we feel it connects us with a past that we have no knowledge of. Legos could prove such an artifact in enough time. Fifty years or one hundred years from now scientists could study the art of Lego sets but that all depends on how you feel about it's importance.