I have a Perfection double glass that is 15+ years old and it sounds great, I have always used sandpaper on it (60 grit).  I go up and down in the same direction.  Do you keep the tip of your striker roughed up as well, I use either 220 grit sandpaper or some box call chalk on the tip.  If not the tip will eventually look like they have been buffed to a shine.