It's strange, because your first description is exactly what it does. In each activity you can add a set of widgets and use certain applications, you can even configure the way the desktop is shown (Search and Run, Folderview) differently for each view.

I usually use two different Activities named Work and Fun. In Work I have my text editors, konsole with multiple tabs, a couple of widgets related to those apps, my work email and maybe some books for reference. In Fun I have the web browser, Ksudoku opened and widgets with jokes, rss feeds, email, weather information, etc.

It's easy to notice what I have configured: a distraction-free environment to focus on my work and a distraction-full one to relax; just two clicks between the them! Couple this with the Pommodoro technique (25 minutes, 5 minutes play) and KDE has made me a very productive and happy worker.

Hope my example helps.