by Deefer
Casting an improper face-down enchant could definitely be of major strategic advantage. Imagine someone who's already used up all their teleport traps casting Chains of Agony face down on a zone to discourage their opponent from moving in. That could totally swing the momentum of a game.
Then you cast a dispel on the facedown enchantment... it's revealed as an invalid enchantment and you are refunded your dispel cost (because it is not a valid target). Take another action.
The bluff portion is no different than a handful of decoys, and the loss of the illegal enchantment/2mana/action makes it a highly risky thing to do in the first place.
I still don't see it as a problem that needs fixing.