Well I think the main advantage to the new curses are the lack of necessity for runes. Most people don't want to waste 3 inventory spaces on spells that require a "hit" to work, which is most affective when wearing armor with a positive mage bonus. Now you can tack on draining the opponent's prayer to prayers that depending on your activity, you would most likely use anyway. With that said, I think that a revamp of the modern spellbook might be a good idea, but in terms of practicality, the new curses allow for a much better window of opportunity.