Digital music: About mp3 bit rates...

About mp3 bit rates...

I have quite a number of mp3 files ripped from cd's on my computer at 128kbps. These were ripped LONG ago when I didn't know any better and now I'm wanting to change them to 320kbps. Some of them have longer silences at the beginning and so I could use Audacity to fix that and then re-export them at 320. My question is...can Audacity pull the rest of the "music information," for lack of a better term, from the compressed 128kbps file and make it REALLY 320, or is it best just to delete the files that were ripped at 128 and re-rip them at 320? The problem with re-ripping them is that I've sold quite a number of the CD's the songs came from so I'd have to go repurchase them.

Anyone know if all the "information" is there in a 128kbps mp3 file to extract, or is it gone for good?

Thanks in advance!

Clint