this would have been a great shot only for it been blurred, what setting did you have?, i think you should crop out the swans and brighten up the shot a little.what i would have done is take a shot of the swans at a high iso 400-800 & high shutter speed to get them sharp, then another shot at low iso100 f8-16 and expose for no more than 30″, then composite them in photoshop, just an idea to get them both.
Great opportunity in this shot, but its is let down by bieing too purple, not straight not having sufficient mid ground interest. Simply by getting lower, the swans would have moved up in the fram, filling more of the midground. That said, a good crop and bit of reprocessing to get the cathedral dominant would be worthwhile.
i think you have real cracker there trying to get out, including the swans was IMHO a touch of genius – many people might not have bothered due to the long exposure (i actually think the blurred swans are fine) – agree with b318isp though a lower viewpoint would have cut out some of the wasted midground and possibly let a little more sky in at top
bit longer exposure to brighten overall image might have helped too. i too would be interested in seeing what settings you used