Sorry I'm late to this thread, but a few points I have not seen (or missed) elsewhere:
Glider pilots (gp's) most commonly encounter other gliders, and only few powered A/C, on cross countries. Collision avoidance is almost entirely by see and avoid, not constant position reporting etc.. Listening to FIS's would add little useful data and lots of irrelevant info distracting from the task in hand.
Gliding frequencies generally give useful information to glider pilots - who is finding good conditions where, etc. Most gp's monitor those, or switch off. In any case, carriage of radio in class G is not mandatory, of course.
Crosscountry workload is not comparable with power x-country flying - both demand skills but in different ways. When thermalling, extracting the maximum energy needs constant attention. Between thermals, one is like a power pilot who has lost his engine and needs to do something about it pretty quickly (in our case, find another thermal, hopefully close to track, and use it).
The law on gliding use of radio is a bit of an ass. Theoretically AIUI we are supposed to use our allocated channels only for air-ground position reports. In practice we use 130.1, 130.125 and 130.4 for air-air transmissions. The latter is used primarily for cloud flying to avoid collisions and for general cross-country flying, the others mainly for various specific purposes (training and competitions). 129.975 is for gliding aerodrome calls, limited to 10 miles and 3000 feet. 129.9 is only legal for ground-ground for gliders (other air users have it for ground-air). Gp's can use the gliding frequencies without a licence PROVIDED that the apparatus cannot be switched to a non-gliding frequency, so not for 760 channel Icoms (not a lot of perople know that, and I suspect it is honoured more in the breach than observance).
Increasing numbers of gp's get radio licences as it is becoming more useful for various reasons. At my club, operating at North Weald a lot, we have to have licences to talk to the tower so most solo pilots are qualified.
My club's other site is Ridgewell, just outside the Stansted CAS, and we have a letter of agreement whereby we notify when we are flying and they advise potentially conflicting traffic (virtually all GA going round the CAS, almost no inbound/outbound movements) if they can find time. My colleagues mostly don't normally monitor Essex Radar. I am an exception - I often do, when flying close to the CAS, partly because I spend some time in IMC or close to the edges of the CAS. Once when taking photographs over Haverhill, just below the 3500 CAS, I heard them routing someone round their CAS towards me. I tried to call up to advise my manoeuvrings, and was told to stay outside CAS and virtually shut up and not bother them with my unimportant call. They apparently have time to talk to spamcans going round them but not gliders.
I use to be chairman of the BGA Airspace Committee, and I worked with the Competition people to improve task selection so that comps. would not normally take fleets of gliders through instrument approaches in open FIR (as it was then) or too close to CAS. Unfortunately, as in most fields of human endeavour, sometimes mistakes were made and unfortunate tasks were chosen. Even so, there are penalties for gp's who bust airspace during comps. and for non-comp. pilots who do it in pursuit of other gliding achievenents - GPS loggers have made it easier and more effective to police. GPS has also made it easier to avoid CAS in the first place.
For landing at essentially powered A/C aerodromes, I call up when I can, and so do many others. (In practice, it is rare to do so - maybe 5-8 percent of my outlandings have been at such aerodromes - it's far more often into a farm field). If someone is non-radio and has to land, I believe they are in the position of being the commander of an aircraft with a legal responsibility to minimise risk to to crew and aircraft; the aerodrome may be their safest option at the time.
Hope this helps.