depends on your playstyle

ussualy u should have enough but it never hurts to increase it

Generating rage allows you to use your dragon more often. More dragon use allows it to level up faster. So it can be very important. A warrior will want strong dragon fast, since he generates more rage for it naturally. A mage will likely spend most of his rage on Ball lightning and mana accelerators, so it isn't quite as important. The paladin, as is to be expected, is somewhere in the middle.