I reckon it is totally nuts to rewrite/rearrange 300,000 lines of code just because the UI is a bit dated.
Also, you should consider the effort required to make sure that you haven't broken the actual (non-UI) functionality. Clearly, more changes - more risk - more testing.
Open the old project in VS2010, make sure it compiles (not trivial as the C++ compiler has been made a lot more compliant and hence stricter), and then start fiddling with some UI elements.
Start from the most obvious, ancient things first and work your way up from there.
True colour icons (like in the toolbar) as opposed to crummy 16 colours will be a nice first step and sometimes provide a step change as to how the application is perceived. Get feedbak from supervisors and users. Then take it step by step.
I can just see software purists coming out at me with all guns blazing