Separate Niche Sites vs Portal vs ??

Always hear about a successful website is to focus on a niche, which is understood as important if anyone is going to spend money on advertising. However, trying to apply the niche model to a "town portal" is quite perplexing, unless perhaps I am missing an ingredient.

For example, if you research keywords for your area, you can pick a specific industry, restaurants for example, that give a reasonable number of searches and CPC. And, the competition for the keyword, YourCityRestaurants, in search results is weak, at best, with the exception of the big directories, such as TripAdvisor, Yelp, etc.

So, then you build a website dedicated just to restaurants in your city, YourCityRestaurants.com, for example and with some work, being unique, it could move near the top of the google search.

Then you move on to the next niche in your area, lets say Attorney's. Same gig, you built a second website, YourCityAttorneys.com.

And so on.

So, now you have a bunch of individual websites for your local area, which certainly now is not a portal.

The alternative is to have one town portal, YourCity.com, with categories for each industry (restaurants, attorneys). However, as a broad website, you lose the ability to improve the ranking.

Is there an alternative design to get the best of both worlds, Niche bebefits + Central portal ?