Is a 3-day Uyuni salt flat tour worth it?

Yes, a 3-day tour is highly worth it in practice because it lets you actually see the Eduardo Avaroa Andean Fauna National Reserve, where you get bright lagoons, geysers, and hot springs that you really cannot get to on a 1-day trip.

On the other hand, a 1-day tour concentrates mainly on the salt flats and the Train Cemetery, while the 3-day excursion goes further, into the Bolivian Altiplano. That longer route gives you a deeper geological and wildlife feel, including glimpses of Andean flamingos and these unreal rock formations. Plus, it is the most practical method to make the border crossing straight into San Pedro de Atacama, Chile.