Aside from the training for my multi rating , and the occasional recurrent training since, the engines have both been operating...and probably will be for the next several thousand hours. So it's not about the ability to handle an engine failure.

Actually, it is. If you desire to fly corporate aircraft or airline type aircraft, you are looking at aircraft with more than one engine, more complex systems than a light single, and things are happening at a faster rate. But all in all, its also about the decision making, which ONLY comes from experience. Also, the engine may be great, and running like a champ, but if you ingest a goose or two, it wont be for long...And, you still need to fly the aircraft!


"Is "multiengine time" a pseudonym for "time in heaver, complex airplanes?" Or is it assumed that twins are more "serious airplanes" than "little airplanes" like C172s and that time in twins is therefore probably more representative of what employers will pay me to do?"

Yep, that's mainly the point. A Cessna 310R, which is mainly a light twin, is more challenging to fly than a light single engine. It is about insurance, but it also depends on what your career goal is. Recreational, corporate, airline, military, etc. Anything past recreational or military you will need both time and experience because the majority of the flying is predicated on multi-engines.