Besides the obvious things most humans share, such as people who care about them, special needs give us a sense of appreciation that others lack. For example if someone has lost certain abilities he or she usually develops a vastly greater appreciation of the abilities that remain than "normal" people have.
Perhaps the biggest blessing is the way we understand each other.
Although my chronic illness and pain have greatly improved, when I meet someone else with chronic pain or illness and they learn of my experience we connect instantly at a deep level because we share some major life factors other people can't comprehend. The same thing applies to caregivers. Raising foster sons with special needs helped me understand other parents doing the same thing, and my own mother's terminal illness gave me a taste of what life is like for people caring for family members with similar problems.
Sharing the experience of dealing with disabilities, even those that are different from the ones in our own lives, helps us become friends easily.
Special needs give us a lot to be thankful for.