We use "wildest" as "more wild". Example: Durango, Colorado, once one of the wildest cities in the old west, was now the home of 12,000 citizens and one of the coun­try's last narrow-gage railroads. (More examples: http://sentence.yourdictionary.com/wildest). En español: es como "mas salvaje". Ejemplo: unas de las mas salvajes ciudades. Do you understand?

Wildest dreams: It means some one achieved beyond hope, imagination . Even in my wildest dreams, I did not think that I could get admission to Harvard.