I really doubt you'll hear a difference once the files are compressed into MP3s. I have listened to dither comparisons between WAV files before, and unless the music is at a VERY low level, the difference is subtle; there is a deepening of the soundstage with dither applied, like the vocalist and instruments move back a little from the speakers.
I do think, if you are reducing the bit depth of a 24-bit file down to 16-bit, you should use dither.