I find it's only useful to own the alt-coins if your trading on the active markets and follow the bigfish (you have to know who has those large stashs of ltc).  There's ton's of market manipulation but you can make some good money if your sharp. 

I would never consider an alt-coin as a long-term investment, Bitcoin is the best for that hands down.  There may be volatility in it's price but it will increase heavily over time.