They should succeed. They fit the formula. There is a clearly identifiable and reachable target audience. There are a range of issues to get people engaged. There are existing connections between members. There are benefits from interacting with each other. A good community builder should be able to succeed here.
Yet still most fail.
They fail because they either focus too much on the technology, or too much upon news-style content. Technology helps, but rarely hinders. Hampton People, W14, and Harringay Online use Ning, East Dulwich uses a forum. Neither spend more than three figures a year.
And if content was going to succeed, local newspapers wouldn't be struggling. All the communities listed above prioritise interactions over content.
A few failed hyperlocal efforts simply give up before they succeeded. If the examples of Hampton People and East Dulwich are anything to go by, in the first few months you will only be getting a handful of members. Maybe 10, perhaps 20. This is part of the process.
If we want to build hyperlocal communities, we have to change the way we think about them. This isn't a technology problem to solve (Facebook-style). Enabling everyone to start a hyperlocal community wont make it happen. This isn't a content problem to solve (local news style). Pulling in RSS feeds and encouraging user generated content wont solve the problem.
What we need is a genuine community building approach. You identify your first members, initiate discussions, invite members to participate in those discussions, write content about what's happening in the community, and repeat as you grow.