Doesnt Pascal's wager type of argument apply here?
Opening the source has very little benefit in most cases while opening the source presents a very real danger of clones.
Pascal's wager only applies if you simultaneously discount the benefits of having contributors and play up the risks of clones. This seems backwards to me; it would take much less effort for someone to contribute to your project than to fork a new one. As such, you should get more contributors than competition.