Hi Damo,
Is the viewers attention meant to focus on the sunset/sunrise, or the couple ? Think in the rule of thirds for this scene, you need one third above the horizon line and two thirds below. Regardless of the beautiful scene going on in the background, the focus still has to be on the couple. I've attached a very quick work of your image. I've cropped away a little too much from the top .......

Kept the colours to what would more than likely, naturally would be going on, and tried draw the viewers attention to the main couple before they eye wanders off to take a look at the scenery.
Don't forget to straighten you horizon line, so it doesn't look like the water is draining to the right :-)
If the scenery is the important part, forget what I just said