I think that the part you are referring to was a caution about using your radio in a gaggle.
Having been in some 20+ glider gaggles, the radio is the least useful thing you have on board at the time.
Speaking to Scottish quite a lot of the time the guys and girls at the other end are great, One of my buddies gets queeried on his mode s alt fairly regularly, the tone is always gently surprised when he confirms fl120 or whatever he's cruising at.
Some local controllers do have a habbit of attempting to foist a service upon you in such a way that it feels quite rude to decline.
The tone of the bga letter was, I feel, that we are doing ok, keep it up.
Controllers are learning more about what gliders do and glider pilots are getting better on the radio.
encouraging glider pilots to engage with controllers seems to be improving things all round.