The frequency of the updates is a function of the
Sensor Trigger Threshold (Sensitivity) and
Data Rate settings in the InterfaceKit device. The Data Rate setting controls the frequency at which the interfaceKit scans for changes. When using the web service this is locked at 16 times per second. The Trigger Threshold sets the minimum change in the raw sensor value (0-1000) that is required for the new value to be reported. (See the Phidgets
Analog Input Primer for more information).
If you set the Trigger threshold too high for the 1127 light sensor, you will only see significant changes in light level. For example if you set it to 500 you will effectively only see one transition between total darkness and absolute brightness.
If you are seeing the same values in the Phidgets device you created and in the Pref pane for the interfaceKit, then, as you guessed, the plugin is operating properly. Note, there is a sensitivity setting in the preference pane. But, the plugin will override that setting, so you need to adjust the sensitivity setting in the Indigo interfaceKit device.