See Nostromo's earlier fascination with Giselle's feet , and his promise to gain land that she could set her "little feet upon." If those images represented the People trying to bring the ideal utopia to earth, then this one evokes the ideal bereft now, clinging and paying homage to the only force that actually can walk the physical earth -- the feet of the People.
Also compare the profusion of gold upon Nostromo's feet with his desire to get Giselle "a gold crown for thy brow." The symbolic reversal confers upon Nostromo something better than the "heaps of shining gold" that constituted the false treasure of Azuera , or the "gold-mounted rosary" that might have paid Paquita's tribute. It is the true treasure of love and, for the might of the People, the cosmic and paradoxical gift of eternal rulership without wealth.