If it's anything special, it will be copied at some point.
It might even be created without you sharing the idea. I've had ideas in the past that were unique and never shared, and other games came along with the ideas. People generally all have similar thoughts. Because of this, there can be a lot of patterns to everything- and ways people mimick/copy others.
I choose to think that my creativity is good enough that I can continue having unique ideas when old ideas become less unique, etc..
Still, I keep some stuff to myself if I have some fondness for it and know it is high up on unique scale.
So if you are really fond of your idea, and think it is really unique, keep it to yourself. Maybe gain some experience on a less unique project you can share and carry over what you learnt for your more important projects.