Hey, Plenia -
I'm not a big fan of "nicheing" as a tactic - if you keep coaching, you'll wind up finding the type of people you like to work with and that will organically become your niche.
Having said that, one of the best ways of knowing if you are being sufficiently specific in targeting your clients is to ask people "do you know who NOT to refer to me?"
The easier it is for them to answer that question, the more effectively you've identified your ideal clients.
You might like the programs they offer at
www.perfectcustomers.com - if memory serves they're relatively inexpensive and useful when you're first starting out (or looking to take things up a notch...)
happy exploring,
michael