MP3 files to Apple lossless

This is for the digital guys. I have most of my digital files in itunes ripped at 320 and 280 kps. I noticed that there's an option to convert files already ripped to "Apple Losseless." If the files are already ripped at 320, 280 or 190kps is there any advantage converting them to apple lossless, or I is better to redo the whole process and start ripping them from your original CDs.

Thanks in advance,
Tony