You have to be careful with those might vs. certain
Spirit is certain to increase the damage of every spell you cast (30% spirit -> spellpower).
Crit might increase the damage of some of your casts.
Still, most Moonkin value crit > spirit. If not, consider dropping Nature's Grace, Vengeance, Eclipse, and Nature's Majesty from your build, since they aren't
certain to increase your DPS.
If you were to gem Wintry Endurance with Rigid+Veiled (which I don't recommend), you'd still be above the hit cap. Your SP would be about 17 higher, your crit about 14 lower. 17 SP > 14 Crit, and that is using a bad gemming combination just
to remain hit capped.
Barkhide -> Wintry (+Rigid+Veiled)
+1 SP, +3 Int, +49 Spi, +5 Sta, -15 Cri, -4 Hit (but 275-4 Hit is still capped)
+49 Spi (+10% BoK +2% IMotW) * 30% (IMkF) -> +16.5 SP
+3 Int (BoK, IMotW, Lunar Guidance) -> +0.4 SP
+3 Int (BoK, IMotW, Int->Crit) -> +0.9 CR