If one is really concerned with weight and wants just a little something to smooth over cracks there's a product that I use a lot. It's called Skyloft. It's lighter than any glass cloth, works with just about any glue or paint, and it's quite strong. It's also pretty darn cheap.
There's an old axiom: one can build a plane to fly or one can build a plane to crash. The lighter you keep it, within reason, the less likely you are to crash.