The only ones that are "needed" IMHO are BTC and LTC.
In the same sense that the only social networking sites that were "needed" were Friendster and Myspace. Or the only web browsers that were "needed" were Mosaic and Internet Explorer.
I think that it won't be long before BTC and LTC will be regarded as the first-generation crypto-currencies that blazed the trail, but the technology will move past them. Proof-of-work designs in general may go out of fashion.
It's seems to me many people do not see the possible changes that may happen. For example, instead of looking at BTC, LTC, XPM as alternatives to USD, EUR, Swiss Franc, etc, see it as alternatives to nickles, pennies, cents and Dollar. BTC to buy a house, LTC to buy a coffee. Crypto currencies are not going to change finance, business, purchase methods. It will revolutionize it into something we have never seen. Just how FB took social networking to another level. I agree on BTC and other PoW designs will witter with time, they where just first.