[Micah]

Alright, maybe an autowin only applies to LE Ermor, but the following will sure get a lot of mileage out of Utterdark:

Dreamlands would probably do pretty well with it, all the real troops have darkvision 50 or 100, they have freespawns, and by the time they can get it off their population's gonna be pretty beat up anyhow, so the income reduction hurts a lot less.

Agartha: darkvision and solid death summons to avoid the income hit (they also have a great incentive to take death scales, so again, later game the income hit will kill the income gap between them and growth players). EA agartha at least also benefits a heck of a lot from halving enemy defense skills, and tends to be heavy on sacred troops, so upkeep hurts less.

Any blood nation will similarly have darksighted demons and a mediocre economy, and I don't think blood hunts are impacted by the utterdark.

Any nation with reanimation.

Other nations will have more problems with the income hit, but if they know they'll be casting it they'll have the advantage of having a gold reserve, and can leverage the darkness to help their troops out:

Yomi/Lanka and Shinuyama: More darksight.

Aquatic nations in general tend to have darkvision, and even if they don't I'd take a 5 attack wave warrior against a 10 defense van over a 10 attack wave warrior against a 20 defense van any day, and archers pose much less of a threat...again, when you suck already you're a lot better off if everyone else sucks too.

Plus there are the random attacks on enemy territories that occur, which is never a bad thing. I think that's a pretty significant list of nations that can get some use from the spell though.