Cool idea. My dad had low vision and we used the adhesive dots, Velcro and colored tape. Be wary of putting something directly on a button as setting the device down could result in an accidental press ( like turning off the tv).

In Canada, our ILS Specialists usually do use puff paint for marking things and drawing tactile diagrams. They are especially useful where adhesive dots don't stick so well (one common location is putting a dot of paint just above the key slot for a lock, so you can feel the dot and line up the key).