Note: Please click on these images to enlarge them - the panos don't look as good in the native resolution.
Armed with the wonderful suggestions from the CiC members, I went out again last night to do a re-shoot of Centre Block and the War Memorial. The problem turned out to be a focus issue (i.e. don't trust your camera's focus mechanism at night), so I used a magnified LiveView method suggested by some of the members. I also switched to the f/2.8 14-24mm lens for the shot as the f/2.8 24-70mm was a touch too long to handle the shots of Centre Block.
The lighting was completely different than when I shot on Dec 23. I know that sounds a bit crazy when doing night shots, but it is none-the-less true. We had snow showers late in the afternoon and after they cleared, the sky started to clear up and rather than a constant overcast, the background was more patchy.
War Memorial:
Centre Block in Christmas colours:
100% scale - Outtake of East Block showing the improved focus:
Again, thanks for all the suggestions / thoughts on what went wrong on my first attempt!