> and am usually the person being approached for advice and mentoring. I never found the efficiency of the process to be lacking

That's a good exmple for GP's point: deliberate, premeditated interaction works just fine remotely. But everything else falls away. That talk amongst the almost random subset of meeting A that happens to be also in meeting B and walks from A to B together, things like that. Occasional random peerings are powerful and a company chatroulette would be an awkward substitute.