OD Channel Reducer allows you to reduce keyframes in multiple channels of an item at the same time. The plugin is a generic plugin:

Options:

• Reduce Position (x,y,z) : Defines the position envelopes you want to reduce the keys of
• Reduce Position (x,y,z) : Defines the rotation envelopes you want to reduce the keys of
• Reduce Position (x,y,z) : Defines the scale envelopes you want to reduce the keys of
• Reduction Tolerance : Smaller values keep more keyframes than larger values

Here's a how-to video showing OD Channel Reducer in action.