If you don’t want to use Multisite, yet still want to have multiple blogs with a common backend, another idea is:
- Customize your theme’s Author Templates so each author’s “blog homepage” has a distinct design
- Create several different stylesheets, one per author. Use some conditional logic to display the appropriate stylesheet when viewing an individual blog post, so that the post matches that author’s homepage design.
- Create several different sidebars, one per author. This will allow you to have different widgets per author. You’ll need conditional logic to know which sidebar to display too.
Of course, this would require quite a bit of tweaking too. Multisite might be less work.