I didn't think that removing doom had anything to do with skill level, just luck. I've used cursna on whm with little skill (I know... BAD WHM!), and my wife used it on hers with capped skill, and we both had about the same success rate.
And I always thought that cursna just removed curse if you were cursed, no questions asked, unless it was a different curse (like the difference between silence and mute). (I misread you... I thought you said cursna OR doom, however, I struck it out because I like it as a stepping point for this next spell idea). On a similar note, we need a doomna, or a "insert -na spell here" II that removes the higher tiers. Maybe an Erase II that can erase doom or amnesia.