Interesting results in the poll so far, seems like the vast majority of people feel that this would be the ideal size, and then you've got an equal amount of "outliers" that want either bigger or smaller.
Very nice setup you got there on your SE, it probably comes closest to what I am envisioning from the currently available choices on the market.
I am getting 404 lbs wet no fuel for an SE with a 2-into-1 ti pipe conversion, how much weight does your fairing add? Or did you measure it full of fuel and with bash plate, hand guards, shark fin, stabilizer, frame guards, axle slider etc that you would have to add to any other bike weight as well?
The additional weight savings should come from 10 years advance in manufacturing and design, as well as the smaller displacement and lower stress on the components. If they manage to save 5.5 lbs from the 2011 530 (510cc) engine to the 2012 500 (510cc) engine, the savings going from the 2003 DOHC 950cc to a 2013 700cc-800cc (SOHC?) should hopefully be around 20 lbs. Then downsize the frame and swingarm, get rid of the front tank and subframe and replace them with a plastic underseat tank subframe and you should hopefully save another 20-30 lbs. You will also have to carry a lot less fuel, if you compare a F800GS and your SE with a modern FI system and engine design a 30% reduction is easily possible.
50 lbs is not quite as dramatic in savings but surely noticeable (fuel tank and how the weight is carried is another improvement), and your SE is already completely optimized compared to a standard Adventure, where the difference would be much greater.
I'd be willing to make the trade of a bit less power for a bit less weight and better economy, taming down the beast so to say, and making it more manageable for mere mortal riders like myself.