Sharpness at night

I'm taking shots at night in ambient light, and I'm experimenting with ways of getting sharp images. Currently I'm using ISO 800, and have started being more methodical about using a tripod to eliminate motion blur.
Having said which, I'm still not happy with the soft shots I keep getting. I realise it's a tough environment in which to get sharp images, and I don't expect miracles, but I was wondering if anyone had any hints on how to improve my chances of sharp shots at night.
These are my attempts so far (some sharpened to one level in Adobe CS2):

Having said which, I'm still not happy with the soft shots I keep getting. I realise it's a tough environment in which to get sharp images, and I don't expect miracles, but I was wondering if anyone had any hints on how to improve my chances of sharp shots at night.
These are my attempts so far (some sharpened to one level in Adobe CS2):



