Yes the added value is limited, as it is for most applications. Actually in many automation solutions you need more energy to supervise your automation system than the efficiency gain 
With Miele, there is very little you can set or change in your appliances (apparently for safety reasons), it is useful if you get to know when the washing machine has ended (you don’t have to remember to look at the watch or to set an alarm
Unfortunately the Zigbee protocol defines certain aspects of technical communication (frequency and so), but not the protocol used, so just because they are both Zigbee devices doesn’t mean Hue and Miele can communicate with each others. That’s why all Zigbee devices need their own gateway. However, Hue would speak WiFi if it hadn’t been disabled by Philips.
Yes Miele is moving away from Zigbee to WiFi, but apparently it still needs the XGW3000 that gathers the data and sends it in a standardized way to every machine that wants to be kept informed.
The best source - where even Miele engineers are participating - seems to be the Symcon Forum. However it is in German.
