Depending on how you code, you may see a productivity increase. For background, I'm also a long-time vim user, but I learned emacs about 2 years ago, and now use them interchangeably.
What drove me to the point of actually learning emacs was its useful ability to have a large number of files open at once, and to easily switch between them. I was in the middle of introducing a feature that added and touched a large number of classes. (This was C++, so there were typically two files per class.) Since I was still firming up the interface, I would typically be in the middle of updating one file when I would realize that I needed to change another.
With gvim, it was easiest to open a new window for each file, which was starting to get unwieldy. With Emacs, though, it was simple to open a new file in the same window (Ctrl-x, Ctrl-f). Once Emacs has a file open, it's very easy to switch back and forth between the open buffers (Ctrl-x, Ctrl-b).
Taking that one step further, a single emacs session may open many windows, so in addition to splitting the window vertically, I could decide, without interrupting work on a file, to open another next to it, letting me effectively work side-by-side while still keeping each window at the default 80-character width.
There are still some things that I find easier in vim (e.g. block-select mode, simple macro recording, diff mode), and things that are easier in Emacs (line alignment, file/buffer management, window/screen management). Therefore, I find myself alternating between the two (and sometimes using both simultaneously), depending the editing task I anticipate.
If you're still unsure, I'd suggest trying it out. Run through the Emacs tutorial and then use it to write code for a morning or a day, leaning heavily on the help. If you still don't like what you see, stay with vim. Regardless of what the editor brings to the table, your familiarity and knowledge of the tool will by far be the most important factor in your productivity.
