A good overall balance can sometimes make a difference between a decent plane and a great plane. I've drilled holes in the wing tips of a couple and epoxyed lead in to balance them laterally. It doesn't take much. Just set the plane up on whatever means you have to balance with and just set the weight on the tip. Once you have the correct amount just take a hammer and whack it into a roundish shape. Find a drill bit thats close. Drill the tip. Tap it in place with some epoxy or whatever glue ya have and brush some paint on or a bit of covering and no one will ever see it.
The majority of your flyin it won't really be noticable but some manuevers and certain planes will really show the difference.