In Habitable Planets for Man (Elsevier, 1970) Stephen H. Dole identifies 42 stars within 22 light years of Earth that are candidates -- although only 14 of them have (in his estimation) odds of having a planet in excess of 1%. One way to confine exploration is to plop Earth-like worlds down at all of them, give all of them sapient inhabitants, let half of them advanced technological civilization, a quarter of those superior to ours; and put No Trespassing signs everywhere.
There are a couple of things I don't like about this. The most significant is that space shoudl feel empty. It's one thing to say that it takes 6 months to get to Alpha Centauri; it is quite another, and more powerful, to play through plodding through systems with nothing in them but rock-balls until you get to something interesting.
Still, some parts of this idea is good. If Space is just plain empty of complication and competition it can get tired pretty quick. There has to be variety somewhere -- in one direction, open frontier; in another, unpleasantly advanced aliens nearly on our doorstep.