At the moment there is only one privilege for welcome pages which controls the ability to access the Welcome Page Designer itself. However once in the designer there is no way to stop a user editing/deleting system pages as well as personal pages.
The privilege for the designer itself is: Configuration Components -> Configuration -> Designers -> Welcome Screen.
You could certainly raise a suggestion to extend the control for these. I do know in 7.3 there will be full publishing available for welcome pages (now called Dashboards) similar to shortcut group publishing but I don't know if the privileges have been enhanced too.