As for me - i see two ways to evolve your referral system. The first way is to post your referral link everywhere you can and get a lot of referrals. Following this way you will get some profit but, as you said - it can be a lot of referrals without any profit. The second way is to invite your friends or just active users. This way gives you good profit per referral but the quantity of them willn`t be huge.
I can`t say what way is more profitable, but don`t like users that use the first way and use the second way by myself.
Both ways can work perfectly if you can spread in the right websites with so many people interested in the things you promote. I have already seen those both ways before but it needs patience to get good results. Usually, people spread your referral links on social media which they have many relationships with people out there to help them get many referrals. Facebook will be a good example of this as I still see them promote their referral link on that site.
Of course it is so. Social media gives a huge quantity of referrals but i think that it is often not fair because most often the link is hired and you become a referral and even don`t know about it(if the is fair - i think that this is correct and join it by myself often). But lots of men think that this is ok, so i willn`t argue with them - this is their decision and if this is ok for them - my opinion costs nothing.