Struts to Spring Migration happy, Java

amy

I am currently managing an enterprise application based on Struts 1.1 and SOAP for back end communication.  The application connects existing mainframe functionality, through a Java front end, with a web based interface to serve forms and reports.
Back in 2003, this was enough to keep everyone happy, however trying to modernize the front end to include latest technology widgets, dashboards and visual functionality is a near impossible task.
Considering your experiences, what do you feel is the best approach to migrate to the Spring framework, in a staged approach if at all possible, and leverage the latest UI tools?
Primary considerations are:
-  Maintain the SOAP transport
-  Make the UI more limber and maintainable to allow for quick changes in look and feel, as well as graphical interaction
-  Simplify!  the Struts environment is a bear to navigate and maintain
-  Through this migration create an application environment that is more easily maintainable and agile using Eclipse tooling