Is there a music player for Windows that will let me speed up / slow down my songs? I can do it for each song in Audacity, but that's too tedious, I don't want to resample my entire collection to new files, I just to listen to it in a bit more higher-pitched version.
VLC Media Player.
Can adjust playback speed up or down, including fine adjustment.
Windows Media Player can do this just fine. There's a panel which you can activate. It will not pitch the song higher, though! It will just go faster!
To activate: Go into the Windows Media Player menu (ALT), go to View and Extensions, playback speed.