I agree that this is probably too much. Modern languages are training us to ignore the semi-colons; to have to pay attention to the whitespace around them seems retrogressive.
To be fair, the semicolons in Nulan are mostly used as infix operators, unlike in languages like C where they're required at the end of every statement. And Nulan already uses significant whitespace indentation. So I don't think it'd be a lot worse to make the whitespace significant for ":" or ";" I just think it might be a bit too far.
