On: How do you encourage users to share/copy/evolve data while preventing competitors from copying it?

If I understand you correctly, you want people to be able to use your data for whatever they want except to compete with you. So why not just make everyone agree to some form of a non-compete with regards to the use of your data? Just leave it broadly defined with the right to terminate their license at any time if you feel they are violating the provisions or spirit of your TOS.

I don't want anyone to get a copy of a significant portion of the data. Moreover, I don't want competitors to use any of the data.