Well... actually in 4e you took a pretty decent hit by converting your items back and forth to residuum to make them into 'whatever'. Also the default items you were assumed to have at a given level were 2-5 levels ABOVE your level, and thus not subject to being reenchanted into something else. So this was really a non-issue. Anyway, item rarity did away with that, giving the GM a vote on what you could make (and the default is no, you cannot do it). Enchantment rules in 4e are there simply to let you create some weird items you just really wanted and the GM for some reason never got around to, or if there was some specific item that was going to be REALLY beneficial in a specific plan or something, so you could make it just to use that one time.