I seem to suffer the same 'you can't see to hit' attack rating reduction in the dark whether I am under cat's eye spell or not (or maybe I just don't know it at a high enough level).
You get a lower penalty (Target partially obscured by darkness vs. heavily obscured). The spell level only has an effect on the duration on the spell. To remove the penalty, combine Cat's Eye with Predator Vision (or just use Predator Vision on its own).
