If the pictures you're taking are coming out all black, it sounds like your issue lies somewhere in the lens assembly or the sensor itself. The matter of being "worth fixing" is up to you, since it's difficult to place a monetary value on the environmental impact of manufacturing a new camera and throwing one away.

Now, to climb off my soap box, digital photography technology has taken leaps and bounds, and $150 today will get you a camera that takes better pictures than the digital camera my dad spent $500 on in 2004. Just make sure that you properly dispose of your old one; most stores like Best Buy have E-waste bins at the front of the store.