he is asking for a reason to think it has benefits that exceed those that can be obtained at other kinds of events

Or, rather, that exceeds that that can be so obtained. That is, SB's7b relates to the relative quality of the reason for belief, not the relative quality of the benefits.

But you're right that (for example) Christian retreats routinely get people to volunteer to do things and do them, so the simple fact of a Minicamp attendee doing so is not by itself strong evidence of a difference between the two events.

OTOH, there may well be sufficient differences between the two communities that the similarity of results is such evidence. That is, if event X1 gets result Y1 from a member of community Z1, while X2 gets Y2 from a member of Z2, the similarity of Y1 and Y2 given significant relevant differences between Z1 and Z2 suggests equally significant differences between X1 and X2. If Z2 is consistently more inclined to cooperate than Z1, and Y1/Y2 demonstrate willing cooperation, I conclude that X1 is more effective at inducing cooperation than X2.

(OTOOH, a lot depends on why Z2 cooperates more reliably. If it turns out that cooperation is primarily caused by the quality of Z2's events, then that's evidence against there being a significant difference between X1 and X2.)

Yes, after I said "After Minicamp you will be able to explain the math behind what you do", thus answering the original question, whereupon I was directed to answer other questions instead.