I have a DS with the same sensor. You do not want to under expose in low light conditions. Push to the right of the histogram without blowing the highlights.
Which noise reduction are you using in PSP? I prefer the Digital Noise Removal over the One Step Noise Removal. I usually just use the DNR default settings.
Also, did you sharpen you image after you finished all of your other post processing? For the web size versions, I like Unsharp Mask with one of these two settings
a) Radius @ 1.0, Strength @ 100, Clipping @ 0
b) Radius @ 0.75, Strength @ 75, Clipping @ 0
Here is your second image using setting (a)
For full size images, I like to use some high pass sharpen (Radius somewhere between 1 and 3).
Tim