"And to the other issue of glider ballast, no, heavier aircraft means faster glide without range penalty. So if you want to win the glider race, you'd better carry some sand."
Hmmm, all the gliders I flew carried water ballast. The theory behind carrying water ballast is that the increased weight shifts the drag curve to the right and thus minimum drag speed and thus best L/D occurs at a higher airspeed. Ballast is used early in the day when lift is strong and fast glide speeds are more important than being able to climb fast. (remember increased weight increased the descent rate). Later on in the day if lift strength decreases, the water ballasts is dumped to decrease the descent rate at the expense of speed at best L/D.
I maintain that the statement that weight does not affect the glide angle is an oversimplification. This is true if one considers only induced drag and the vector diagrams. However, this is only part of the story and does not take the increase in profile drag (form, skin friction, interference drag) into account at all.
For relatively small increases in weight it it generally true that the glide angle is unaffected. However, if you were to increase the weight by say, a factor of 4, I am sure that you would see a significant decrease in the glide performance.