I do not understand why you spend time and resources to this competition. Common bounty campaigns like facebook, signature, twitter and telegram already proved yourself. Moreover, it is not likely that someone will come up with something more effective.
I actually think that the competition is really good idea because it increase chances to find new ways of bounty campaign promotion. Moreover, it is not so costly as you think.
What is the competition about and how will it be structured? If it really rewards those that are actively promoting the project by producing valuable content its great to have.