Pagerank and SERP Ranking have very little correlation to each other - don't believe me? do a couple searches and you'll often find sites with less PR outranking sites with a lot of PR.
I would most definitely use the Site's Age/Existing Authority to rank for the new terms.
In terms of Site Navigation, make sure that the new niche you're targeting is in a folder one level below the root domain (e.g.
www.domain.com/newniche).
To further leverage the power of your root domain, I would do the following:
On the homepage of your website, I would create contextual links within some relevant content with your primary and secondary keyword.
If you want to rank that one page for various keywords (which is very often the case) do the following before you embark on your link-building frenzy:
Code:
<a href="http://www.domain.com/newniche.html" title="primary keyword">
<strong><em>primary keyword</strong></em></a>
and
your secondary keyword the same but add a # to the end of of the page's url like so:
Code:
<a href="http://www.domain.com/newniche.html#" title="secondary keyword"><strong><em>secondary keyword</strong></em></a>
Why, you ask?
You can leverage the
SEO Strengthof the existing site for a few keywords instead of one.
Google have a first link counts rule whereby the first time a URL is encountered on one page, it is the only time it's associated with it's anchor text or actually counts as a backlink; if you use the same URL on one page numerous times with lots of different anchor text, it will have little or no impact after the first time it's used.
e.g.
Code:
<a href="domain.com/newniche.html>keyword 1</a> - this one will count
<a href="domain.com/newniche.html>keyword 2</a>
<a href="domain.com/newniche.html>keyword 3</a>
<a href="domain.com/newniche.html#>keyword 4</a> - this one will count
Using a # tag is one way you can override this rule as crawler registers it as an entirely new URL and you get to create two back links which should help you a fair amount in terms of SERP Rankings.
Anyway this should actually help you a fair bit when starting out for your clients niche.
Any questions or clarification needed, just ask!
Good luck
