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.

What kind of project are you looking to do?  Do you have any specifics? There are several use cases that can apply blockchain to agriculture.  

Not a bad idea.  But speaking fees are driven largely by celebrity/publications status more than anything else.  If they don't fall into one of those two categories then compensation may need to be reconsidered.  I recently chaired a conference for IEEE and we had some high profile speakers, but paid no speaking fees at all and only compensated travel for a couple of them due to distance.  It is the policy of IEEE and many other organizations to NEVER pay speakers!  Adopt the same policy and you'll level the playing field pretty quick!  There's always someone else just as good - unless a certain speaker is needed for a strategic/marketing reason. 

One of the IEC (International Electrotechnical Commission) technical committees (ISO/IEC JTC 1/SC 41) which serves the Power Utility industry, are working to incorporate blockchain technology into IoT solutions, which could serve as the backbone for Smart Cities projects and others.  This work is still relatively new however.

It is important to note that International Technical Standards take time to evolve, because they are developed by large groups of representatives worldwide who must all agree on the standard and support its adoption.  Indeed, such standards are often shaped by early adopters themselves who have the most experience. I would encourage anyone interested in such standards to get involved and become a part of the process - your input is needed!

Standards are also important because many highly regulated industries, such as Utilities, are very standards driven.  Contributing to such standards can help accelerate adoption of blockchain in these industries.

There are also standards organizations dedicated to Blockchain, one example is BiTA, Blockchain in Transport Alliance.  

Provenance (tracking of goods) and Regulatory compliance seem to be the most important use cases related to supply chain, and these can be broken down into several sub-segments.  

By documenting the provenance of goods as they move thru the supply chain, the breadth of recalls can be reduced and problems within the supply chain can be more readily isolated, diagnosed, and resolved.  Regulatory compliance can be verified as goods move thru the supply chain as well (inspections, quality controls, etc).  Tracking of goods can assist with inventory management and inventory tracking, especially when components are manufactured in several different countries and assembled in another.

As for change in practices, blockchain will demand more digitalization of the applications/processes at the various steps within the supply chain.  For example, there are often delays at import terminals/ports due to missing paperwork (bills of lading, etc.)  By going digital, this information can be transferred in real time so that terminals can plan and execute more efficiently without compromising privacy.  But this, as do other scenarios, will require shippers, receivers, etc. to digitalize their information, and/or export their information into the blockchain system via an API.