1) Why wouldn't 320 VBR with minimum 320 be at worst the same as 320 CBR, and possibly better if a particular passage warrants it?

2) Is there a general consensus between Lame V0 insane and 320 CBR, as to whether they are equal? In another forum, it was stated that Insane is the same, except that it only allocated less if the frame is quiet or "inaudible," whatever that means. I suspect that the matter must have been settled here by now.

320 k vbr doesn't exist because most decoders are limited to 320k frames - thus CBR 320k is the strongest working setting. If there was no frame limit, VBR 320k should have been better than CBR for obvious reasons. 320k minimum VBR would probably activate Lame INSANE setting.

Insane should be stronger than V0 for reasons stated above, but much less efficient as bitrate cannot rise or fall. Also it will use a more sensitive hearing curve.

if you need the highest possible quality lame can offer use the insane preset. if you want to get slightly smaller files with minimal quality loss, use -V 0. no need to add other switches like setting a minimum bitrate.

Does Lame no longer have the ability to use 32kbit frames for silence when the bitrate is set to 320kbits?

Try --abr 320