Great idea! I propose changing the full curation bonus to a so-called 'delayed' full curation bonus . After 3 months of the referred user signup, a full curation bonus from his/her posts for a specific time period (perhaps 4 weeks) could be activated. This is because after signup most users stay minnows, struggling to become dolphins. But after 3 months, good quality providers become minimum dolphins. This way the referring users are motivated to bring valuable bloggers.
I am speaking from experience: when I saw that at busy.org I got 10% of my referrals rewards, I was excited. Then I saw that was valid only for the first 30 days....and ahhhh ...what a minnow could do in 30 days...