An action is special "for" me. An object/place/person is special "to" me. "Returning to my home country was very special for me." "She gave something special for me." "My home country is very special to me." A) You are special to me --- is correct "useful to" is used when saying it is useful to a person. Ex: The information was useful to me. "useful for" is used when saying it is useful to a thing or cause. Ex: The information was useful for the project.

For special, it's A). When you say, you are special to me, you are using the pattern of person X is something to you (~ means something to you). However, there are sentences where for is correct. -> He bought something special for me. > The pattern is: he bought something ____ for me. Could be anything else, like gross, pretty, etc.

A) You are special to me B) You are special for me A sounds good to me. A) it's useful to me B) it's useful for me both sound good to me