Haven't really looked at the age changes. But seems fair...
Though 50-60% success rate means more effort any way you look at it. Like you pointed out yourself, NM is predominantly an early-war spell. Rune (at least past early age) and wizard sustain isn't too much of a factor. Guess the rune cost really could come in handy to deploy NM strats earlier in the age than otherwise possible though. That's a pro :)