I generally agree that re-sampling a 128K mp3 at 256K is silly and pointless with one caveat: if the re-mp3 software has any sort of filtering, it may be able to get rid of noise in the original file. Overall quality will be technically worse, but subjective quality might be better. (Of course, you could still just resample right back to 128K in this example and get the same results.) I don't know of anything that actually does this though.