I'm not sure what foobar 2000 doesn't do.You could drag in all your music into a playlist, enable the "bitrate" column on your playlist, then you can sort by bitrate. Initial playlist building takes a while (but my music collection's at ~100gb). I'd also recommend having a 'codec' column enabled and since I'd suspect mp3/cbr may have lower bitrates at little loss of quality
Mine looks something like this so sorted. I wouldn't do it this way though
There's a smarter way to do this -
You can also use search (ctrl + F) to select these out (which I wished I knew before I messed up the order of my music) - you can find a more complete guide to the query syntax here, or by clicking in that ? in search. You can even copy paste these to a new playlist. or further filter (for example %bitrate% LESS 320 AND %artist% HAS nirvana), so you know which tracks to rip again.
I'd add its a great, flexible music player, with a lot of awesome options. It'll run portably if you didn't want a permanent install, and all sorts of great plugins.