I cannot for the life of me find out where the files for plugin changes are located.  For example, I changed a reverb and modified it slightly.  I save the change using the plugin window. If later I want to uninstall, restore from backup or move my Cakewalk install to a new computer,  I want to keep my custom plugin settings.  Where are the files associated with my saved custom plugin?
 
Or is there a way to "export" the plugin data so that I can "import" the same plugin saved customizations into a new install or backup/restore of Cakewalk?

It depends on the plug-in. The Cakewalk DX plug-ins save settings in the registry and the plug-in manager provides an export/import facility.