Audacious 3.2.3 on Mint 14 (installed from Ubuntu repository) does not seem to use the replaygain values stored in mp3 files. Replaygain does appear to work with FLAC encoded files. I think I’m going to complile from source and see if the problem persists.
Please note that Audacious is nothing to do with the Audacity project. You will need to raise your issue with Audacious http://audacious-media-player.org/ .