And what sort of deck would find Wood Elemental useful? Are you going to tap four of your lands and then sacrifice three more for a mere 3/3? Four mana for a 3/3 is already bad... Presumably, you could make it more efficient by going to a higher number. But how? Tap four lands and sacrifice ten more for a nice, big 10/10? If you have 14 lands in play, there are tons of other cards that can potentially win you the game without utterly wiping out your board position. Great Wall is a horrible card because it costs three mana to do absolutely nothing (even more of nothing than Snowfall). That is better than paying four mana to hurt yourself. Great Wall is a 3/3 four 2W under Opalescence, which is not at all bad. Wood Elemental is a black mana with Songs of the Damned and not much else.