Will Wilkinson notes that happiness cannot be taken as the sole master value and pleas for a “reasonable pluralism” in which happiness competes with other values in the public debate. I agree that happiness is not the only valuable thing, but I also think that happiness has additional merits that go beyond its intrinsic worth. One extra point in favor of happiness is that it matches other humanistic values quite well. A second bonus is that happiness is an indicator of the fit between living conditions and human nature and, as such, informs us about the practicability of various value mixes.
Pluralists look for policies that produce an optimal mix of the various values they endorse. As a result they must consider how well these values match each other when put into practice, and will give priority to values that appear to fit well with others. This requires some insight into synergies and conflicts between values. For years, moral philosophers have tried to gain this kind of insight with mere armchair theorizing, and have typically focused on possible conflicts. In the case of happiness, this kind of theorizing has produced dire scenarios such as Brave New World, which suggest that the pursuit on happiness will violate principles of freedom and human dignity. But now, empirical happiness research allows us to look at actual conflicts and synergies between values, and this creates a different picture.
The available data provide little evidence of conflicts between happiness and other values, but instead show synergies between happiness and the values typically endorsed in contemporary Western nations. People live happiest in societies where humanistic values are put into practice, that is, in societies where human rights are respected, the political system is democratic, the educational system fosters independence, and where a decent material standard of living is enjoyed. So, the means for furthering happiness are typically things we value in themselves as well. Moreover, happiness is also instrumental to several of these values. For instance, happy people appear to be more likely to live up to humanistic values than unhappy people: they are not only more autonomous but also more social and creative.
This is not to say that happiness fits well with all values. For instance, people appear to be less happy in societies where collectivistic values, such as submission to authority and identification with a clan, are endorsed. The main reason seems to be that humans have an innate preference for a fair degree of independence. 
This brings me to the wider point that happiness is a sign of human thriving. In most biological organisms, flourishing is manifest only in physical health and survival, but in higher animals it is also manifest in affective experience. In humans, that affective experience is reflected in happiness. As such, happiness carries important information for a moral pluralist. It tells us whether a chosen value mix is workable or not. If people live long and happy lives in a country, then the value mix is apparently viable there. If not, the mix must be failing to meet the objective demands of human nature in some way and must therefore be reconsidered.
For these reasons happiness deserves a prominent role in the theater of value pluralism.
 Alexandra Maryanski and Jonathan H. Turner, The Social Cage: Human Nature and the Evolution of Society, (Palo Alto, CA: Stanford University Press, 1992).