I have just come across a new feature in Camera Raw called Super Resolution.
There is a video from Julieanne Kost on YouTube that explains all.
I have yet to try it for myself but it looks as if it may be useful for making larger prints (or DPIs) from smaller images.
Norm found it too, and gave it a whirl, but it takes about 5 minutes to process an image!
It looks, from various comments, that you have to open the image from Bridge to access this feature