It will improve your marketability
A few people have been asking this type of question recently. I wonder if it is a trend of former technical people who turned project manager wanting to go back to their roots? With increased pressure to deliver more in less time, I would not be surprised if project managers are bearing the brunt.
However, there is a good case for refreshing technical skills in IT project managers. Technology has moved a long way in the past few years, and although I would argue that everything changes and yet remains the same, I know that in recruiting project managers a strong, current technology background would carry a lot of weight.
I would advise people with programming skills to broaden their skill set by gaining a better understanding of the business in which they operate. Equally, it is valuable for a project manager to get back "under the covers" of delivering IT solutions. If you do plan to move that way, with your experience of the industry and knowledge of your own skills and aspirations, I would think you are well placed to assess the benefits.
In terms of which technology path to follow, I would agree with your choice. My view is that a good C++ programmer should be able to turn their hand to any language with relative ease, and the object-oriented focus does add weight to the perception of the skills you would have. Given that background and new skills in Java, I would think you would be well placed for a technical future and that will in turn improve your marketability as a project manager.
Solution by Terry Watts, E-Skills UK
The panel: MSB International, Best International, BCS, Computer Futures, Computer People, Elan, Reed Computing, Netheads Consulting, Zarak Technology, E-Skills UK