That's a good point. I was thinking about it from the perspective of Earth-launched debris, which would usually be traveling somewhat the same direction, as it's the cheapest orbit in terms of energy expenditure.
Not really, since lots of satellites have technical requirements for polar orbits or are otherwise not following the least-energy, eastward orbits. Even if two satellites are traveling within 5 degrees of the same direction, their relative speed is still over 1,000 mph. (LEO speeds are over 15,000 mph.)
