So after invading a narrow penninsula with terrible terrain, you invade an even more narrow penninsula with roughly the same terrain? Not exactly a stroke of brilliance on the allies part.
Not to mention this would almost have to pull resources away from D-Day. Air power, naval resources and men. Guess the only positive side of this would be(from the Allies non-hindsight point of view) is this would be somewhere to dump Patton off where he couldn't get himself into much trouble.
In hindsight, the only positive things this would have achieved are possibly bringing Romania and Hungary to our side of the Iron Curtain. Of course with a slower liberation of France that very well could push a bigger slice of Germany, if not all of it, behind it.