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.