I have never heard of or seen a site that uses different template files per style.
But I guess it could be done.
It's how I envisioned theming working in v7 (as opposed to styling)...
As for the topic at hand, once you start tearing templates apart you are going to forefit your rights to support from the powers that be, they may still work with you, but they cannot support 3rd party code modifications. That being said, that's what UBBDev was made for, but you're not going to find much info on v7 for making a theming system.
You can style quite a bit with the default editor,
www.agardenersforum.com or my
Development Forums are both stock as far as the style goes, everything is done with CSS. Though none of them are stock, I modify all of my sites.
