Per T155038#4299441 and Peter Southwood's approval via email, it would make sense to disable upload to non-admins (while keeping upload enabled to admins). See T129845 for the reason I would prefer it restricted.
Wikimania wiki series is not a content wiki with any sort of community, therefore no Community-consensus-needed. Approval from Wikimania organization team should suffice. (I can forward the email if desired.)