You owe it to the community. If it hadn't been for other members who saw fit to donate their money, time and energy, the synagogue would not exist. If you don't reciprocate, it can't continue to exist. You owe it to yourself. Synagogues are the places where the communal activities of Judaism come alive.
Worship services are just the tip of the iceberg.
I realize that no individual can participate in every aspect of Jewish community life, but few people are as active as they could be. If you want to make the world a better place, then join a social action project at your shul. If you want to meet other people who share your Jewish outlook or Jewish values, then attend a social event or volunteer for a committee at your shul. Browse the synagogue's library. You owe it to your children, and everyone else's children.