You could add certain evolutionary alterations to the wings to give them some purpose.

- The wings could develop marsupial-like sacks to carry young ones. When the mother tucks her wings in, the babies are safe from harm, and when they want to get out, they can just extend.
- Dragons will have great momentum while running. The wings can be used like parachutes, to stop the dragon quickly if needed.
- They could have spines or spikes, enabling the dragon to fight by swinging the wings around.
- The wings could have mural-type decorations for mate attraction.
- The wings could be used for swimming. For this purpose, they may evolve small air sacs, enabling the heavy dragon to remain afloat easily. It could also use the wings as oars to propel itself.

The possibilities are endless, really.