From what I can see, it doesn't seem to be allowed to edit the full version of Sunset Valley in CAW, which is annoying.
The .world file for Sunset Valley is located in 'C:\Program Files\Electronic Arts\The Sims 3\GameData\Shared\NonPackaged\Worlds\Sunset Valley.world', however, you'll get
this error if you try to load it by conventional means.
All I can see is that you're able to edit a "lite" version of Sunset Valley and Riverview from 'My Documents\Electronic Arts\The Sims 3 Create A World Tool\UserToolData\Worlds\Sunset Valley_lite.world', but it will not be the full version of the town. I have no idea why they decided to include this but not the original town.
Sorry if this isn't any new information to you, CAW is a pretty new tool and nobody really fully understands it yet.