I am tearing out old plaster walls. Are there any uses for this rubble? I hate to see it all go to the landfill if there is some use for it. Could it possibly be used for filling low spots in my yard, covering it with topsoil of course? I also have a gravel driveway that I might expand, could it be used as a base for the gravel?

Sure, two good ideas. We have buried drywall. There are claims that it is good for the soil but they have been discounted, but there's no harm in it, and old plaster won't harm it either.
Wish I could have done that 30 years ago, but had only a postage stamp city yard and driveway.