Agreed. Long exposure to show movement works best when there's really only one thing moving. E.g. clouds or water or people. If there's too many things going on then it just looks blurry. I would try to winnow it down to just a static subject and those clouds, which turned out beautifully with the colors.
I would even take things further than rogue's suggestion, and crop out all the green (preferably by moving the camera all the way up to the edge of the water). The bright green grass (almost yellow in places where it's well-lit) just kills the mood. You could have a beautiful shot all composed of purples/pinks/blues with the water reflecting the sky, the pier and bridge in the middle, clouds and sky in the background.
Looking again at the palm tree, I think it could make a good subject (even with all the movement) if it were completely non-illuminated, i.e. just a black silhouette against that lovely smear of clouds.
Also, at f/8 and long exposure the lens you're using isn't necessarily going to have to be the greatest IQ in your bag. I probably would have used a zoom lens covering the same range that would have given more ability to zoom to compose.