I should make it clear that I don't intend to invalidate the work of all the playtesters and designers with my comments. This is a truly tricky rules situation in a game with a metric crap ton of interactions. Even with such fringe cases, I still think MW is one of the greatest games I've ever played, and I really appreciate all the hard work that went into making it what it is today!
Has an errata to Seeking Dispel been considered? What if "Controller of enchantment cannot reveal the enchantment once Seeking Dispel has been cast" was replaced with "If the target enchantment is revealed before Seeking Dispel's Resolve Spell step, destroy it anyway"?
EDIT: ahh, that still wouldn't work because you could reveal an enchantment like Healing Charm to get its effect before it was destroyed. Hmm, how about "Treat Seeking Dispel's three casting steps as if they were all one step"?
EDIT #2: But then Decoy dies without giving mana. Okay, I give up.
I liked kich's explanation, actually - "Destroyed" triggers still happen even if an enchantment is facedown when it's destroyed. That allows stuff like Cantrip to work too.