I am currently working on a very large legacy MFC MDI application. It has a large number of UI elements - dockable toolbars, custom tree controls, context menus, etc. It i
FWIW, in the interim, you could use the MFC Feature Pack (available with VS2008 SP1) to give your app an Office 2007 look and feel pretty quickly (you can even add a ribbon if it's something your users would like, though this would be more involved.) I revamped the UI for an old MFC app using these new classes in a single day and now, to be fair, it looks fantastic, and my users are very pleased (you can support a whole host of looks and colour schemes.) MS opted for the BCG toolkit, but there are others available if you want to pay a small amount of money (CodeJock for example.)
I know this doesn't answer your question but if it's just UI changes you're after then it might be worth a look.