You can make a client side html with lots of js, css and images and call the web services server (arduino + ethernet) with JSONP. The server side code could be the same for 3 ot 15 devices since you can encode the the device no in the web service call. I did that and it works on most browsers and devices.
Would you share your code for using the JSONP method? please
I have been thinking along the same lines; serving a fancy webpage from an actual server, and just fetching some simple values from the arduino, to include on the fancy webpage.