With regards to sharpness, yes the majority of my night time photos are HDR.
Sharpness begins with the lens and its optimum aperture. For most lenses, shooting between F/8 and F/11 will give you the sharpest images. For my night shooting I'm almost always around F/9 -F/11. If there is more depth to the image (things far in the distance) that I want to be in as much focus as possible I'll go to F/11. Once in a great while I'll go to F/16 because I want more starbursts on the lights but sharpness does suffer a little bit.
My 50mm F/1.4 lens seems to be much sharper at F/2 than other wide open apertures.
Another thing is to pick what part of the scene you want to be the sharpest focus and make sure you are right on it with a focus point. When I'm shooting night shots on a tripod, I actually go to Manual Focus and put the camera in Live View. Then, using the zoom (on the screen, not the lens) I zoom in as far as I possible can on the area that I want in focus and manually focus on that spot. In the shot of the right above of the couple watching the fireworks, I zoomed in on just the window of the castle to really dial in my focus.
In terms of post processing, you're going to laugh but the last thing I do to my photos (other than putting my name on them) is in Photoscape. (the free program) My last step is usually to go to the drop down menu on the Bright,Color tab and to Contrast Enhancement - Low. Then I go to the Sharpen drop down and hit 4.
The only problem with doing this in Photoscape is that it affects the entire image and will add noise to your sky. Most of the time I end up taking the sky from my -2 exposure image and layering into the image so it is very clean and I'm not worried about adding noise to it. Or, depending upon the image, like if it has nice white fluffy clouds and a pretty sky, I'll do my Contrast Enhancement and Sharpening and save that as a different image. Then I'll take the previous one that has a cleaner sky and layer that sky back into the one I sharpened. I know all of this could be done faster and easier in Photoshop but I do think that the sharpening tool in Photoscape works much better with less noise than Photoshop does.
Hope that helps.