Perhaps we could have a custom JIT notification (in the avatar drop-down, with the other notifications) that is triggered if you receive more than X separate Like notifications in a day. It would say something like:
Woah, everyone likes you! If you’d rather not be notified about every like, you can change that under “Notify when liked” in your [settings].
I think we need some built-in discovery aid for fringe settings like these. It’s not relevant to 99.9% of users, but to the 0.1% it is quite critical, and it will cause them great annoyance if they’re never made aware of the setting’s existence.