Pace, I'm sorry you got frightened by a glider in IMC outside controlled air space. However, that is an extremely rare occurrence.
ESPECIALLY COMPARED WITH the number of times we glider pilots get frightened by power pilots with their noses in the cockpits, not looking out at all at all. And the number of times our gliding sites are infringed by light aircraft and helicopters. In fact we had to file an airprox this weekend, as a BIG BLACK HELICOPTER on his way to Wellesborne passed at 500 feet above airfield level directly over our winch operation, which typically dangles a braided steel cable from the glider at l400' down to the ground. Not to mention the other 3 gliders soaring over the airfield above the helicopter who also observed the idiot. Wellesborne tower told him to phone us, he did, and apologised that he had been looking at his GPS map at the time, too bad he couldn't read it!
Over time, it may cheer you to know that most gliders collide with each other and not with you GA chaps (crowded thermals, you know). The only midair between a glider and a GA aircraft I am aware of in 25 years of paying attention to accident reports was in VMC. The K13 glider landed safely, despite losing a foot and a half of wing. The power plane, which had hit the glider from behind, unfortunately did not.
All your FLARM, TCAS, gadgets and controllers still do not absolve the pilot of the duty to see and avoid.