I must say that I am really impressed with all the deliberate thoughtfulness you are putting into the project... and it gives me a lot of confidence that you are building something that will become a lasting presence, not just as part of Hive, but in its own right.
Referral fees are a good thing as long as the rewards remain contingent on the person(s) being referred actually participating. One of the issues with many referral programs tends to be that they can create a huge number of "dead" accounts that only ever take one action: Signing up.
I don't know what the technical end would take, but perhaps on way to increase referree participation would be for the HoloZing infrastructure to include what no other Hive dAPP effectively has: Effective internal messaging. If I can refer someone, know they have signed up with my referral code, and then be able to contact them "in game" to encourage them to get further involved and/or just help, that might be a great feature.
Anyway, keep up the good stuff!
Good ideas, maybe we can make use of sting chat in the game since everyone will be required to have a hive account in one way or another connected.