I remember someone saying they sped up the bitrate display for MPC to make it look more 'alive' From what I remember, they did it by editing a file to do with the plugin.

Is this a possibility, or am I deluding myself? If so - is it possible with other codecs, Vorbis & APE in particular... both have pretty slow update speeds, which is one of those little annoyances to me

There is a file inside the Winamp plugin folder called "musepack.ini". There you will find the entry "UpdateBitrate=7". Change it so it fits your needs.

A value of ~35 updates once per second, and lower values update faster.

Aah, I guess that only works for MusePack then... as I don't have an ape.ini or vorbis.ini