"3) Do breakers 'wear out' or degrade over time? One reason I want a
240V circuit is I'm experiencing nuisance tripping when running my
table saw under load. Is it possible that the breaker is just tripping
prematurely?"

Yes, they do wear out over time. Usually it manefests itself in the
form of not tripping as fast as it used to or not tripping at all. The
previous reference to Federal Pacific was incorrect, their two pole
breakers are infamous for not tripping. This person is experiencing
nusiance tripping. Big difference!