I still feel Notify on every like should be the default … I have this enabled on meta and do not find it too disturbing, even when @zogstrip goes on a like rampage. You can set it to be the default on your forum and experiment to see if it helps.
The idea is that if new users are notified more on likes they are more … like…ly to like.
That said, a lot of this would be due to the type of forum or type of participants. Some cultures, forums, people are more likely to like and some are less.
Some forums, in fact, hate likes so much they disable them.
I am not even sure that “not enough liking” is a pathological problem. Not enough good content, not enough active users is the war you should be fighting and it is somewhat controversial to assume “more liking” will get you “more and better content”