Some 17s are lighter than some 16s. (I don't know what "unsprung weight" means, so if there's a difference beween that and plopping wheels on a scale, I'm talking about the latter.)
I'm going with 16s. I think they'll have 45- or 50-series tires on it. I cannot imagine going with a lower profile tire would be beneficial in 99% of my driving. I can imagine the rougher ride of 17s having ill effects on the car's components -- or my components.
As for brakes, GTI brakes will work with 16s. Anything larger than that on a 1900-pound car has got to be overkill.
Larger wheels and brakes do increase the wow factor -- at least with me it does. There are just so many different road types where I live, I can't have the ow factor surpassing the wow factor, especially with minimal (at best) benefits.