Ávila is smaller than Toledo and most places shut down fairly early, so the town lights shouldn’t be much of an issue. However, if the walls are lit up, then they might hamper your gazing. About a half mile from the wall is the Cuatro Postes overlook. You should be able to get in some nice viewing. If you have a rental car, then a little further away from the walls, like from Mirador entrada Ávila, might be better.
Toledo is a different story since it is larger and is more lit up at night. I think a good place to observe the night sky would be from the Parador outside of town. Again, if you have a rental car, drive over to Guadamur (20 minutes) and park by the castle and chapel of Nuestra Señora de la Natividad. In that location there will be few if any lights at night.