"(Personally, I view with sadness the generation of street musicians who believe it necessary to use battery-powered amps"

I view them with annoyance whenever I go downtown. I'm not too keen on the accordeonists who have been there every day for the last 10 years or so playing the same songs, either.

"but the crooners were loathed, loudly and often, by the previous generation of singers"

I'm not sure this is historically accurate or it might at least not be the full story. Possibly the first crooner was Gene Austin, who had been a singer on stage without a microphone and wasn't loathed, but was one of the most popular singers of his era. He found many imitators, presumably also people who used to sing without microphones. I could imagine that many singers were very happy to have something that would make their jobs easier and also make more subtle interpretations possible.

"If the venue's got a lively acoustic, drop the mikes"

Please don't encourage mike dropping! Those things are expensive and fragile. (I do know what you meant.)

Without amplification, it's very difficult to achieve balance and I don't think, for example, a concert with a clavichord, i.e., an instrument whose sound has been described as hair pins dropping onto the floor, in even a moderately-sized venue could possibly work without amplification. Without amplification, when an dulcimer goes head to head with a banjo in a contest of volume, bet on the banjo. To say nothing of string basses.