How can I restore the springs in my storm door hinges?
Door closing hinges I've used in the past have had a tightening mechanism. At one end there is a grub screw and a series of holes in a ring where the spring is joined to the base plate.

You loosen the grub screw and use an Allen key to increase the tension on the spring.

This should mean that the door closes (at least for a couple more years).

Be careful not to tighten it too much or you might have problems pushing the door open against the spring or it will snap back very quickly indeed.