Well, killing your own skeleton to kill an opponent's dragon would be a bit silly, but perhaps the cost could justify it.
However, this card has more applications than you think. Not only would it duplicate the benefits of buffs, you could play it offensively and double the effects of any single target spell. But to make things interesting, it could also be a defensive card. Play it on your own strong card and their strong card, and they won't be so willing to try and take out your strongman anymore.