I just re-read my post and realized that I forgot to say explicitly what I did, and why I did it.
Basically, rather than trying to find a general procedure to reproduce in PS all the color, tonal, vignetting and other changes that the Instagram filter makes to an image, I realized that for very soft images like this one, a much easier, and certainly equally viable alternative is to simply up-rez the small Instagram image to the size needed, and introduce some fine detail in the high rez version to fool the viewers' eyes into thinking there is more detail present than there really is.
This is done all the time for advertising posters originally shot on DSLRs instead of high megapixel medium and large format digital backs. You'll often see this approach used in woman's clothing stores - they turn what would normally be a very soft image (after enlargement / up-rezing) into a grainy pop culture "look" that becomes part of their branding.
HTH,
Tom M