Can you explain to me, why you are blurring the whole image after adding the noise? Especially because you seem to be so concerned about sharpness...
I'm not. I'm only blurring one of the noise layers to filter Photoshop's noise function so it takes on the appearance of larger, organic clumps instead of the exactly-pixel-sized noise particles you usually see from Photoshop.
Also I don't get why you try to reinvent the wheel. You might consider reading Schewe's article upres article
Although the noise section is pretty basic, the sharpen and upscaling section really gets down to the point. Schewe rightfully uses bicubic smoother
I use Bicubic Sharper because it brings out more image detail without increasing the noise level, unlike your example. I tried both, did the comparisons, and chose Sharper based on the results. I know it's technically "backwards", but I'll take results over theory any time.
One of the design principles of the action is to leave the after-action image in a state visually equivalent to the original--if you compare the after-action image at 50% to the before-action image at 100% in Photoshop, they will be visually indistinguishable. This means that noise levels need to be kept low (to keep detail from being obscured), and tonality and overall sharpness are not altered.
Your version of the image is sharper than mine, but you've also sharpened the noise well beyond what is needed to disguise upsizing artifacts. If you want to do additional sharpening after upsizing, do it only to the the original image layer under the noise layers. That will accentuate true image detail without simultaneously sharpening noise.
After that, he applies Photokit's Super Sharpener, which is the same method described Fraser's sharpening book as Texture Brush. In principle it is just a sequence of USMs with decreasing radius and increasing increasing amount.
I've been using that as a general sharpening technique since 2003, see http://www.outbackphoto.com/workflow/wf_20/essay.html
for a description of the my original action set, and http://www.visual-vacations.com/Photograph...ningActions.htm
for a more recent version. Lately I've been using Focus Magic for deconvolution-based capture sharpening, and then my midtone actions for creative sharpening.