No this is a bad idea. This is an open source project, and thus an open source community. Meaning everyone regardless of skill, age, or what ever should be encouraged to share, even if it is the "hello world" equivalent. I agree it can be annoying.
I've often found myself "tilting at windmills" at graphics forums trying to persuade people from falling for the siggy bug, a click of so called graphics artists who produce nothing but signatures using copy pasta of other people's art, but alas that is a loosing battle.
You can however, appeal to people's sense of individuality, by making a specific part of the forum to deal with this, perhaps a subforum under creations. In this subforum you could allow users to post their ghost shooter clone. Hopefully those with any sense of creativity will see the hundreds of duplicates, and be inspired to make something else. Also, this way if someone does go off the path, and post a clone where it's unwelcome, the thread could simply be moved.