CodeFN42 has released VeloScaler, a free MIDI utility plug-in for Windows.
VeloScaler is a VST plugin that will let you adjust velocities of MIDI notes. You can set a minimum and maximum value, and scale the velocity by a specified percentage, which can be randomized.
Use up to 5 different bands, based on either the incoming velocity or the MIDI note number, with different settings for each band. This can create interesting variations if your destination instrument is set to respond to velocity.
The plug-in is available to download for Windows (VST).