Maybe someday, we will be like China and we won't need a strong currency. But right now our entire economy is based on our ability to borrow money and that demands a good credit rating. If the dollar slips too much we may lose our credit rating and wind up up the creek without a paddle.
A weak Dollar is only useful when you're a net exporter. That way, you're competing abroad in marketplaces and making as much as possible.
When you're a net importer, however, a strong Dollar gets the most bang for your buck. You can literally buy more stuff with it and keep the savings at home.
The United States currently has a very high national debt and the only reason that our government is able to continue printing money is because the dollar is respected worldwide. If the dollar becomes too weak, then the United States will no longer be able to pay off debts or purchase oil with U.S. dollars.
A weak dollar boosts exports, and with the economy floundering, there needs to be every sort of economic stimulus out there. A weak dollar means Europeans and Asians will found our goods cheaper and buy them in greater quantities. A strong dollar all but kills that, and that is not a good thing.