There are two tiers of many of the enchants, the differences are fairly minor. If you really think you will not upgrade an item until the next content patch, then yeah, you should put the better enchant on it. But its fairly easy to get into naxx pugs, and stuff from KelThuzad (or Obsidium Sanctum 1 dragon, Malygos, etc) are quite a bit better than crafted/early naxx drops and do definitely deserve the better enchant, since there is no better item in game.