I don't know if this has been considered before, you could make happiness change your LP learning rate, say 100% happy = +20% learning and 100% unhappy = -20% learning. I think this makes sense because if you enjoy what you're doing you're more likely to take something useful away from it.
The only problem I see with making this change (not that I've thought out all of the implications) is that there aren't many things that alter your happiness yet.
discuss