At 320kbps you are pretty close to the size that FLAC compression would produce, so at that point you might as well go lossless even if you can't tell the difference (at least you could get back to wave files that way). Also you may not have "tin ears," because I've found it takes thousands of dollars of audio equipment to tell the difference at 192kbps. However, any true audio file will say do what you think sounds good (even if it happens to be the tape deck in your car), it is only the snobby ones who are douche bags.
FLAC often has a bitrate higher than 1000kbps, so there is a significant difference between the size of a 320 version and a FLAC version. So it takes about 200% more storage space, takes 3 times as long to copy, etc. That being said, if possible, I'd still go for FLAC, especially for important things (original work, a rip of a rare CD/LP, etc.). With FLAC, you can always make lossy derivative copies, but if you start at 320kpbs (let alone 192 or, god forbid, 128), you will never get better sound from that source, it will only get worse. So if it isor whatever, go for FLAC, other
