It's a good thing for your site to have a main focus. It will give you a niche readership that will follow your site. If you try to make it too broad and put everything up then you will have a lot of visitors but none of them will stay around and overall you'll have less hits. If you focus on one group and cover that subject well that group will keep coming back.
I agree with that. I'm currently building up a city specific site not only with articles but with members. A certain number of people come to do short term research/questions, but you end up with a few that just want to hang around. I want to expand on that aspect.