After you cast Nullify on a creature, the next time that creature is targeted by an incantation or enchantment controlled by an opponent, you must reveal Nullify. If you pay the reveal cost, that spell is countered. Either way you discard the Nullify. Dispel targets an enchantment, not the creature, so Nullify won't trigger.
That's the interesting tradeoff between enchantments and equipment. You can invest in an enchantment even if you don't have the mana to fully pay for it yet, they're more versatile, and you can bluff with them, but they're also more vulnerable.