With emerging technology such as blockchain you may need to keep the door open for a while, as the most value-added projects are still yet to come. Value-add may be difficult to gauge for many early-stage projects. It may be a good idea to monitor the progress of individuals (members) on their projects and ask for regular reporting to ensure they are on track, committed, and engaged in the community - and move them off if they don't make acceptable progress/contribution over a certain period of time. Sponsors may be a bit different....depending on their contribution.