Toby,
Another thing to remember, is that most, if not all P&S cameras have the basic functions already set up, so there probably was a pre-set "sharpening" function turned on and also the camera used a higher ISO number and that also added to the "noise/artifacts" that are in this image. I think your fine up to 11x14 or even 16x20.
I would choose a few of the "worst ones and then get some prints made,locally and see how they look and then go from there,
Rich