This dress is so gorgeous (color, pattern, cut..) on you! I absolutely love it. Like Angie said, it can work at either length. My own eye hasn't adjusted to the midi length yet (still looks a little frumpy to me), so I'm thinking maybe that's your hesitation, too.
You could always wear it as is for now and be on trend, then shorten it when the midi trend ends. That way you can participate in a trend and still have a dress for the long haul when the trend ends (because you know it will!).
It all depends on your comfort level. If you feel unhappy with the longer length, you can go ahead and shorten it now and it will look great.