After having read various materials on sharpening, including Bruce Fraser's seminal work on the subject, I have accepted the fact that I am simply never going to understand it well enough to be facile with sharpening tools. For that reason, I use PhotoKit Sharpener from Pixel Genius for most sharpening needs when using PS.
The problem is that that wonderful plugin does not work for NX. So, if I want to print from NX, I am on my own.
Jason Odell, in his eBook on NX, recommends the following sharpening routine for output sharpening:
Create USM step with settings of 64/2/4 and set the Opacity to 70% in the Luminance Channel; and
Create a High-Pass step with Radius of 2 pixels, change the Blending Mode to Overlay, and set the Opacity to 50%.
He recommends these settings when printing with an inkjet printer on glossy paper for an image at 300dpi.
These settings work pretty well for most images printed on glossy or satin/pearl papers. But, I print a lot on matte paper, and I am not sure how to tweak these settings for matte paper, or how to tweak them for images at 240 and 180 dpi.
A quick piece of information is in order. Your Raw file is a 12 bit, unrendered file. Your printer HAS to have in coming information from an 8 bit, RGB file. Most printers are not capable of handling 16 bit files(but they're getting better at it). It cannot print a raw file as it is not in a color space(be that sRGB, aRGB, ProPhoto, etc) until you render it. In other words, you may be able to print from NX, but it has been converted on the fly to an 8 bit rendered RGB file. With that bit of info, you could do your work in NX, then save out a tiff file to PS(as you know PK Sharpener works within PS)and use Sharpener and it's output sharpening options.
Also, the idea of standardizing on 300 dpi has kind of been replaced with using the native resolution, and if it falls somewhere between 180 and 460 dpi you should be ok. Read Jeff Schewe's artical about when and how to uprez.