To encourage the characters to achieve the maximum level of a particular class i think in addition to acquiring new skills it would be interesting release new attributes to all of the above skills of the same class. As with " Heal " of the Cleric C2, “Zaibas” of the Krivis C2, "Psychic Pressure"of the Psychokino C2 that won new features which greatly improve how the skills behave. This would make the evolution of the classes more interesting and fun.
Sorry for bad English.