Slowrotor,
Airplane pilots and helicopter pilots are trained that adjusting power is one way to change glide angle. But, not the only way. In FW I was taught power off approaches. Changing glide angle meant either slipping or speeding up, or slowing down. In FW, generally if you were slow, and the approach was getting too steep, you would speed up. When I learned to fly helicopters, I was taught to speed up in an auto if it looked like I was going to land short. After I became a glider pilot, it became more apparent why this is so. If you are stuck in a downdraft, you want to spend the least amount of time there. It's kind of like fighting with your wife- you are best off if you can take your licks and get the heck out of there. Any prolonged fight just gets you in more trouble and with less options. So, the less time you spend in the downdraft, the less altitude you lose from it. But, it is a little counter intuative, because while you are speeding up your drag goes up, and you are actually going down faster. But overall you will lose less altitude by spending a short time going down at a horrendous rate, compared to a long time going down at a bad rate. And, when you are through the sink you reconvert the airspeed to altitude.
I have a glider too, mine has no motor. I don't know how fast it goes down with full spoilers. Pretty good though.
-- IFMU