Targeting a niche doesn't preclude you from later targeting another niche and ultimately "general (and bigger) audiences." It intensifies word of mouth effects because people in a niche are more likely to reference each other's buy decisions than in a general market (e.g. if you reach out to military families saying that other military families use it--provided, obviously that this is true--you are more likely to get signup than telling a general population that "families use it."). If you can't target a niche, at least initially, you may need to raise a lot of money to cover your customer acquisition costs.
The two press clippings you cite actually address two distinct niches: global families (families with members widely geographically separated who want to stay in touch), and scrap bookers, people who want to commemorate family events and milestones and pass them along. You don't have general press coverage, you have two distinct use cases.
Pay attention to what you early customers do, in particular the words that they use to describe the benefits of your offering. It will often give you a recipe for a niche. I note that neither "stay in touch with overseas relatives" or "on-line scrapbook to keep in touch" appear on your home page. You might spin it to incorporate one or both and reduce the generic language you are currently using.