I found a program the other night that cleans the crap from your steam game installtions (redist, temp files, etc.). I'm pretty sure I got the link from GAF, it was hosted on google code, but I can't find it anywhere on the internet!
I think it was something like, SteamCleaner, or SteamCondenser (or SteamKondensor).
Edit: Found it! TikiOne-Steam-Cleaner
http://steamcleaner.tikione.fr/en/
CCleaner can do this very thing with the custom Winapp2.ini
[Steam DirectX Installers*]
LangSecRef=3021
Detect=HKCU\Software\Valve\Steam
Warning=Only run this entry AFTER you have launched all of your steam games at least once, as they will not be able to properly load for the first time without these files. After the first launch, however, these files become useless.
Default=False
FileKey1=%ProgramFiles%\Steam\steamapps\*\*\Dependencies|*.*|RECURSE
FileKey2=%ProgramFiles%\Steam\steamapps\*\*\Prerequisites|*.*|RECURSE
FileKey3=%ProgramFiles%\Steam\steamapps\*\*\directx|*.*|RECURSE
FileKey4=%ProgramFiles%\Steam\steamapps\*\*\Install|*.*|RECURSE
FileKey5=%ProgramFiles%\Steam\steamapps\*\*\Installs|*.*|RECURSE
FileKey6=%ProgramFiles%\Steam\Steamapps\*\*\redist|*.*|RECURSE
FileKey7=%ProgramFiles%\Steam\Steamapps\*\*\installers|*.*|RECURSE
That what it cleans.