Once you encode with a lossy format (as MP3, AAC,... but not FLAC and ALAC or WAV or AIFF, which are lossless formats), any further codec changes results in quality loss*. So no, basically, converting your MP3s at this point is a bad idea and won't help. AAC tends to be a better codec than MP3, so using it in the future instead of MP3 isn't a bad idea. A better idea is to just rip the CD to a lossless format and then convert to whatever format is popular at the time.
*(...unless you change from MP3 or AAC to FLAC or ALAC, or WAV which would result in a lossless copy of what the MP3 sounds like... not very valuable, since you would get the same results by listening to the MP3 in iTunes. Also, burning to an audio-only CD essentially converts the MP3 or AAC file into WAV files, which means that your CD contains a copy of exactly like what the MP3 sounds like when you play it in iTunes.)
EDIT: oh yeah, answer the question.