Legal Studies is one of those "interest only" subjects - Business, Legal, Senior Science, General Maths etc. They're designed for people who have a mild interest in something but can't or won't get into a career in that area.
In selective schools we avoid legal studies because it is seen as "the subject to do if you've got no chance of getting into law". That shouldn't dishearten you or anything though - legal s basically dumbed down first semester law, which could be useful if you get the UAI you need.
Economics and Modern History are seen to be very good, because you have to look at trends and think analytically. You also learn to take a wide variety of factors into account when making a judgement. At least, that's what I'm told.