I ran across this link today and remembered it. Very good site.
GuitarNuts.com - Shielding a Tele(tm)
I did this mod about 10 years ago and must say it made all the difference in the world when it comes to noise and gain. Not only did it fix the noise it made the gain of the pickups better.
I used foil tape instead of sheets of copper. The principle is the same IMO.
This shouldn't increase the guitar's gain, so much as allow you to run your amp's gain higher without as much hum.
I did this to my Strat when I last swapped the pickups, but to be fair with a set of Dimarzio Virtual Vintage singlecoils, the hum wasn't exactly going to be a problem anyway.