They will learn who the star is once the same guys keep playing as starters.
Even if you buy a great player, he needs time with the team for the fans to believe he is a starter. Then, provided you keep him outside of the transfer list (him and the main 6-7 players), that fan survey field will improve.
Of course, the more US players the better the merchandise money you will get, but that I think is seperate with the fan survey.