Developing inner values is much like physical exercise. The more we train our abilities, the stronger they become. The difference is that, unlike the body, when it comes to training the mind, there is no limit to how far we can go.
Material objects give rise to physical happiness, while spiritual development gives rise to mental happiness. Since we experience both physical and mental happiness, we need both material and spiritual development. This is why, for our own good and that of society we need to balance material progress with inner development.