^^
Drone, I always interpreted that statement the same way, that Spock was expressing his curiosity in what progress that Khan and Co. would make, not that it would be a hundred years before someone came calling again.
Anyway, some interesting points while I was away.
Why is the Enterprise traversing this empty sector of space?
One possibility may be found in the previous episode, stardate-wise,
Tomorrow is Yesterday. The Enterprise is out of its assigned area because of the time travel shenanigans and is traveling back to where it belongs along an unconventional route. Additionally (or alternatively,) Spock may have chosen this low-traveled area near Earth as a safer place to arrive at from said shenanigans.
How out of touch would Kirk be?
Not very.
Two items suggest this. One, the
Botany Bay is in this sector. The episode consistently references the
BB as an interplanetary craft with "simple nuclear-powered engines" that takes years just to move around the Solar System. Such a vessel would not get very far out into the interstellar void, not in the two centuries that elapsed since the its launch. That puts this sector very near Earth, no more than 200 ly distant and probably a lot less.
Second, the episode establishes that the Enterprise is towing the BB to Starbase 12 at warp 2. So there is a Starbase close enough to travel to at warp 2 with another vessel in tow. Surely subspace radio is faster than warp 2 or at the very least, the communication delay is minimal. With Khan contained, Kirk could wait for the reply.
How prevalent is life in the TOS universe?
Well there is this line from
Metamorphosis:
Kirk: ...and everything's alive, Cochrane. Life everywhere. We estimate there are millions of planets with intelligent life.
And this one from
Balance of Terror:
McCoy: ...In this galaxy, there's a mathematical probability of three million Earth-type planets.
Millions of planets with intelligent life has to mean billions with with just life. So
Timo is probably right,
no life is rarer than
life in the TOS universe, especially if you are looking for a world without it in a place where planets will almost always have it, i.e, the habitable zone of a star where liquid water would be present.
My take anyway, FWIW.