@David the key is to not watch the cards:
You automatically watch cards that you comment on until you uncheck the "watch" checkbox, you only have to uncheck that once.
Thereafter you will automatically watch any card you're added to, but each member can set up this Butler rule that will unwatch any card they're added to:
This means that people will only be notified about being added to a card and mentioned by name in a comment which, in my experience, is the ideal amount of notifications. They can still manually watch cards, lists or boards from time to time as required.
Note that this "unwatching" of cards (as well as centralising notifications and cards you're added to) is one of the core features of my BenkoBoard product:
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