You can still travel to Boliva in the wet season (November to March). Although you may find some delays on the roads, there’ll be far fewer visitors wherever you go, and mirror-like reflections on the salt flats near Uyuni.
The effects of the wet season are more obvious in the lowlands where roads into the jungle can turn to mud and the heat and humidity increase. In the Altiplano, the rains transform dry plains into lush grasslands, but muddy trails and cloud cover can make trekking more difficult and views less expansive.