Nice job at the documentation and description. It should be useful for many users. I have used both the TAOS TSL261 and TAOS TSL267 for monitoring my meter and the TSL261 will be the better choice for most users. the TSL267 is about 10 times more sensitive which requires blocking all background light. Another thing to note is that the Stalker inputs accept a max of 3.3 vdc so connecting the TSL261 to 5vdc might cause problems with the Stalker. It might be better to power the sensor from a pin or use a voltage divider. The TAOS sensors require a minimum of 2.7 volts so the 3.3 vdc from the pins should be okay.
The 100ms delay for the watt indicator light should be okay for most users but will limit measurement to less that 10 watts per second or 36 kwh. I would drop the delay back to 50ms to increase measurement range.
I have rewritten my sketch using some of the code from your example and adding a few other changes. I will post it on the Stalker thread on the Arduino forum.