Not 100% sure how BT rate their exchanges, but I think that green just means that nobody falls below the minimum acceptable download speed.
Acceptable to BT, that is... and from a quick read of the thread, you haven't
Speeds do drop with time, as more people on an exchange get broadband then cross-talk noise in the cable increases, as they go for faster products it increases... not much anyone can do about it.
If your
local cabinet is fibre enabled you might like to look at that, then you only have to worry about the cable from the cabinet to you. My noise dropped markedly when I went to fibre:
Before fibre:
My Broadband Ping
Today:
My Broadband Ping
Can't get actual SNR etc figures from a BT VDSL modem unfortunately.