> Gamers may be fickle, but they are loud and they are loyal.
Zynga. Zynga has made a fortune profiting off of other smaller outfits, just merely by studying and copying. They didn't have source-code (to my best knowledge), but they knew how to make a game mass-appeal. This happens more often in gaming than you'd like to think.
My advice (I work at a gaming company) is to hold all your IP close as possible. Game design, art assets, source code, whatever. You have a right to own it so why not hold on to it for a while until you establish a solid competitive advantage.
On the otherhand, your IP is very closely tied to how well you can integrate teaching. This is something others cannot do easily, so you have atleast that protecting you.