Indeed 192 kbps is enough to achieve near-CD quality, so it's OK. However you should not re-convert your MP3s since each encoding pass will degrade sound quality significantly, due to some nuances of MP3 encoding. Basically that means that path
WAV -> MP3_320 -> MP3_192 will result in a lower quality than
WAV -> MP3_192. You can however recode your lossless compressed audio files like FLAC or APE.
So if you nonetheless want to recode MP3s, save original MP3s if you want to preserve quality for a some other usages in future. I guess you need to recode to use it on a some memory limited device like MP3-player, but hard drive space is almost free these days.