It seems like a good idea to start a thread where we can post techniques for building light. For example, I recently started using Super Phatic glue (from Dave Lewis) instead of CA. It is supposed to be much lighter. I plan to do a couple of tests to see how much lighter, and will post what I learn.
The other thing I've been doing is borrowing techniques from the rubber power folks. I've got Don Ross' book on Flying Model Airplanes, which gives a number of good techniques we can use here. I've also got Lew Gitlow's book on Indoor Flying Models, which has some more techniques, and have ordered his other book "Indoor Flying Scale Models". The point is I'm trying to learn and absorb techniques that will help me build light, but scale electric micro planes.
I also put in an order for "indoor" balsa from Indoor Model Supply http://members.aol.com/indoorMS/IMS.htm.
I'll post if I find that the balsa is better and lighter.