Working with more than one niche does has its benefits, in the long run. At least that's what I think.
A lot of people might say that I don't know what I'm talking about because I'm so new to the forum but I feel that the best way for any webmaster to go is to choose one niche that interest them and become a master at it.
Start with the niche and break it down, for exp say someone chooses "Teens" which wouldn't be a good idea lol but yeah.
You would do it like;
Main site - Teens
First site - Teens Fucking
Second - Teens Blow Jobs
etc etc etc.
And then move on to a next niche.
Learn and know what your talking about, hang out with the people that's interested in the niche your promoting you know.. sure you get the idea.
hope that answers the question.