A number of people I've spoken to have hit the same wall in trying to trace Edward Nicholas. He supposedly travelled to California in 1849 and then kept heading westward to NSW in 1852. My dad (his grandson) was born 7 years after his death but has heard tales of the old man's 'Yankee' accent from his siblings.
Other tales I've heard are that there was a falling out between Edward Nicholas and his parents and that he may even have changed his name to avoid being tracked down. (purely speculation). I imagine that as a struggling gold miner he would have arrived in Australia as a steerage passenger so there seems t be no existing record of his entering the colonies.