find a single example anywhere in computer game or movie history where a court case has arisen from anything remotely similar to mimmicking a game or plot idea.
Capcom sues Data East for cloning their smash-hit Street Fighter 2:
http://www.patentarcade.com/2005/08/case-capcom-v-data-east-nd-cal-1994-c.html
They lost though, so if Capcom with all their legal muscle can't pull it off even in an obvious case such as this, I wouldn't worry too much.