Now that I've had some time to think about it I wanted to write a little bit about the process of physically aging photos. If you've ever Googled the subject you're probably aware that there aren't many resources available. Because of that lack of information I was flying blind with my own efforts, other than the knowledge that most of the techniques used to age paper were probably just as useful for photos. Here are some quick thoughts on what worked and what didn't.
Edge wear- I went over all the edges of the photos with fine sandpaper, paying particular attention to the corners. The result not only appeared worn and shabby, but felt that way as well. I can't overstate how important that is- for props that you're actually going to be handling the texture of the object, the way it feels in your hand, is a big part of it's immersiveness. The appearance of the worn edges was considerably enhanced after I applied a staining solution to the whole photo.
Surface wear- I lightly sanded both the front and back of the photo with fine sandpaper. I wasn't happy with how this turned out, since it looked like...well...someone had gone over the photo with sandpaper. The wear patterns and scratches seemed unnatural. I think the key here is to use a very fine abrasive like steel wool.
Baking- After rinsing off the sanding residue from the prints with water I placed them on a cookie sheet in the oven to dry them out. The heat was set for the lowest setting, around 150 degrees Fahrenheit, and the door was left open a few inches to keep the heat from building up. The result was a very convincing curling of the edges identical to what you find in old photos and a pleasantly aged "crinkly" feel to the paper.
Age staining- I applied a weak tea solution to the entire print. The stain colored the back of the photos quite nicely, and produced a convincing darker stain along the edges, but it just wouldn't stick to the front of the prints. I think I can solve that problem by either using the aforementioned steel wool treatment or spraying a layer of matte varnish on the print before trying to stain it. I'll try both tonight and see how it works out.
Update: The steel wool did the trick. The emulsion still acts as a barrier to keep the paper backing from absorbing the stain, but there's enough "tooth" to it now that the color can get into the fine crevices and produce a nice tint. The prints probably still need a coat of matte spray to make the effect permanent.