I'm thinking about to buy the new Cinema 4D R13. Would be the Prime-Edition enough to build games with Unity or would I miss something special from the higher versions of Cinema 4D (like Studio)?
Take a look at the comparison chart for the versions. Much of what is "missing" from Prime is rendering, particles, etc - basically tasks that can be carried out in Unity. The only thing I'd really want would be the autorigger, but I can't see paying the Studio price just for that.