"The sky is big" is a fallacy in aviation because aircraft don't move unconstrained in 3D space. Typically they are restricted to narrow corridors where collision probability greatly increases.
I imagine the same applies to air commute, considering most people will be converging into a small number of waypoints.
a) you don't have to stick to airways. They're largely for ease of planning and navigation with ground-based navigation aids (NDBs, VORs). You can easily fly off airways, and (in general aviation planes during visual flight) nearly always do.
b) with the advent of GPS, "direct" flight routes (not involving airways) are becoming increasingly common.
c) The "big sky" is not a fallacy. Think about it: first, on the ground you can only drive where there are streets. In the sky, you can fly everywhere (even on a 2-D plane), plus then you have the third dimension. There is plenty of space, and congestion won't be a problem unless regulatory/technical issues impose bottlenecks. Airports are natural bottlenecks, but what is envisioned here are VTOL aircraft, so the number of suitable take off and landing places would multiply.
d) The "navigation paradox" [1] is that improved precision in navigation leads to increased risk of collision, because where in the past airplanes where only approximately on an airway (and would most likely miss each other in case of ATC mistake), now they're precisely on the airway (and will collide in case of ATC mistake), see the case of the GOL and Embraer in Brazil [2]. However, that is a shortcoming of current ATC practices, not inherent in flying.
e) I don't understand your point regarding property law. You can hop on a Cessna at Palo Alto or San Carlos airport and fly over the Golden Gate Bridge, San Francisco, Oracle, Stanford, SLAC, San Jose, with no problem. The airspace is there and it's open.
Bottom line: with modern navigation methods, air space congestion will only become a problem after personal aircraft have become tremendously popular and prevalent, if at all.
I was in what you could define as the "gifted program" throughout middle and high school.
Even though I ostensibly received a more advanced and tailored education, I still shared classes with students much less engaged than I. I was always at the top of my classes and was never truly challenged. I also never had the opportunity to participate in any kind of maths or informatics competitions.
Having never been exposed to excellence, I chose to go to the much cheaper state school (their education will be just as good, the counselors claimed...).
There too I excelled in my classes with minimal effort, took multiple graduate level courses, and received glowing recommendation letters from my professors.
By the time I entered my PhD in a tier 1 university, I was so woefully unprepared -- both academically and emotionally -- that my eventual dropping out was a foregone conclusion.
I spiraled into a deep depression and wasted a couple years of my life playing video games and living with my parents. I ideated suicide almost daily and willfully put my life in danger (standing at the edge atop tall buildings, driving very fast, imbibing liquor until I blacked out).
Now, a decade later, I've mostly come to terms with my mediocrity, but perhaps I could've risen a bit from it had my intellect been properly fostered. But more to the point, had I been exposed to other smart kids and participated in competitions earlier on, my ego could've been slowly molded over my youth, rather than shattered in a few months.
I imagine the same applies to air commute, considering most people will be converging into a small number of waypoints.