In Raiders of the Broken Planet they had a system where for those who paid for certain mission they can use pink tickets when aqcuired to get Blue Mercury point after a successful mission.
Right now I don't know how badly they need money but I believe adding a system to get free Mercury points is only going to hurt general progress for SpaceLords.
In Warframe with there Platinum(Mercury) they have no way to obtain it outside of actual currency and yet they still thrive thanks to there large community and the faith there community has in them.