Pace, couple of points arise in your comments regarding gliders.
The original poster will pick up the point that gliders are often found near cloudbase. In fact if conditions are good they may not even bother to be turning in the thermal, but dolphining along a cloud street. This variation in altitude actually does make them easier to spot, as does the fact they travel in gaggles....if you see one there may be more!
Any glider pilot flying in cloud is probably a professional pilot with the latest FLARM kit. I wonder if the fright you mention with a close call in cloud may have taken place some years ago...
But basically, the glider pilot is flying a craft with superb viz, and is very aware of keeping a good lookout, because they DO fly close to each other.
Though rules of the air require power to give way to gliders, no glider pilot in his right mind would expect the power pilot to have seen him first!