I have read about that experiment before.But i have to add something to it that i read.Opposites attract when they are in their comfort zone.In that auditorium every one were comfortable and at ease so that is why the questionaire suggested that opposites attract..When human are in a situation where they sense they are not secure they tend to stick with similar people..
Yes good people are taken advantage of.You can divide people in three category in this case..1. who will not take advantage and always return the favour(i.e. "good people"),2. those who start out by just taking and not giving,but as time goes by they change(atleast towards the nice people) probably because guilt or some sought of righteousness..3. those people who take advantage no matter what and seem to have no moral compass in their head(may call them bad person)..
I am young and dont have much experience as you sir..But what i have seen is the 3rd category dont exist or are very rare..I have seen many people friends and family members who have changed their attitude when we keep faith and help them without expecting anything in return..All humans have empathy and in the end that is what will drive us to change our behaviour..It will just take some time,faith and patience..
Other then the lady you mentioned i would love to hear your experience on general that whether you have seen good people change others to become good..