Add the ability to create a site from a template within the Worksite Setup tool. By marking any site that you want to use as a template, via the 'Sites' admin tool, with a property called template set to true, we could make these sites available to be copied as new sites. Then, in the Worksite Setup tool we could add another option to the site type screen named 'from template' and if this were selected present a new screen from where to pick a template etc.
I've attached a patch for SiteAction and a velocity template that achieves this. I've also attached some screenshots of it in action.