the WebAii Framework per se is just an API for UI testing.
It sounds like you need the to use Test Studio. Test Studio offers many enhanced capabilities related to test automation. One of these is the DOM Explorer which will let you explore a Silverlight application very extensively.
You can download a Test Studio Trail from your account.
I believe Spy++ only works on certain desktop applications and can't be used for Silverlight. I have very little experience with it so I'm not sure. I'm sure you can find plenty if info on the Internet.
Hope to hear from you soon!
the Telerik team