Use Expressions Controls effects to set keyframes for your wiggle expression.
Here's a quick tutorial video covering one of the most frequently asked questions about expressions in ADobe After Effects. Using the Expressions Controls effects you can link values to keyframeable sliders. This allows you to increase or decrease wiggle values with keyframes. The tutorial also includes how to include the Transform effect so that you can save a Fading (reducing) Wiggle as a preset.
[Edit: Yeah, I know I've changed the name, but my wife hated it and the joke was starting to get old. Plus this brings these videos inline with my other two series, Makin' and Startin']