However, if you build new sites into different sub-niches of the overall niche you specialize in, your overall niche list can do wonders in 'seeding' your new site with potential loyal fans.
A friend just put up a new site and needed a boost. I ran a free solo ad on my related niche list for his KNOW STAGE site (there are 3 stages - know-like-trust) and here are the results within 24 hours of the campaign.
Here are the results. Note the 'before' and 'after' New sites need a traffic boost to jumpstart their overall traffic flow and community formation. The problem is if you don't build a list, you can't get that boost unless you pay for that traffic.
This highlights the fact that you need to get a list going on all your sites. Use that list to provide 'seed' traffic to get a loyal audience base going.
FACT: The vast majority of people that visit your site WILL NEVER COME BACK AGAIN... unless you give them a reason to come back. Your list is the key!
PS. Another reason why you need to SEED your new sites with sub-niche or niche-related traffic is because you can use that established traffic base to grow your site with internal traffic using their 'best content' preferences.