Have you read the Robert Heinlein novel Starship Troopers? It advocates giving the vote only to veterans, all of whom are volunteers. I believe this idea is not in the film of the same name.
If Heinlein's citizenship model existed today, Mitt Romney would be elected in November by a landslide. Rasmussen Reports has polled vets and they prefer Mitt over Barack by 59% to 35%.
It makes sense.
