Having lived under a rock for a while I've managed to miss this great new feature in Gmail: Muting or ignoring conversions
From their help text:
"you've no doubt been subjected to the 'thread that just won't die!' If you're part of a long message conversation that isn't relevant, you can
mute the conversation to keep all future additions out of your inbox."
That is such a smart feature. Interestingly I didn't even think there was a solution to that problem. I sure I have many times needed something like this. Now, let's hope I can remember to actually use this feature.